WO2019056539A1

WO2019056539A1 - Ultraviolet led flip chip

Info

Publication number: WO2019056539A1
Application number: PCT/CN2017/112257
Authority: WO
Inventors: 何苗; 杨思攀; 熊德平; 王成民
Original assignee: 广东工业大学
Priority date: 2017-09-25
Filing date: 2017-11-22
Publication date: 2019-03-28
Also published as: CN107452846B; CN107452846A

Abstract

An ultraviolet light-emitting diode (LED) flip chip, comprising: a substrate (1), and an epitaxial layer structure that is provided on the substrate (1), the epitaxial layer comprising: a buffer and nucleation layer (2), a superlattice structure (3), a heavily doped n-type AlGaN layer (4), a lightly doped n-type AlGaN layer (5), a quantum well active region (6), an electron blocking layer (7), a P-type conductive layer (8), a reflective layer (9), a current expanding layer (10), an insulation layer (11), and a conductive thin film layer (12), which are sequentially provided in a first direction. The first direction is perpendicular to the substrate and is directed from the substrate toward the epitaxial layer. The ultraviolet LED flip chip has the advantages of preventing leakage, having high light-emitting efficiency, having small voltage surge, preventing damage caused by electrostatic discharge, dissipating heat quickly, being highly reliable and so on.

Description

Ultraviolet LED flip chip

Technical field

The present application claims priority to the Chinese Patent Application, filed on Sep. 25,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,

Background technique

With the continuous development of Group III nitride semiconductor materials and epitaxial processes, the output intensity of UV LEDs is also increasing. Compared with traditional ultraviolet light sources, UV LEDs have the advantages of energy saving, long life, low operating voltage, high efficiency and environmental protection; they are extremely important in the fields of sterilization, printing lithography and communication detection.

However, in the preparation process of the existing ultraviolet LED epitaxial chip, the light efficiency is low due to low doping efficiency, poor epitaxial quality, and low carrier concentration of the semiconductor material; and growth of materials such as a substrate and an epitaxial layer. In the process, there are defects such as surface cracks, poor crystal quality, difficult design of structural materials, complicated process, and extremely high precision. In the subsequent flip-chip bonding, solid crystal and packaging processes, there are also large power chip sizes. The heat is large, the heat dissipation is poor, and the etching area is large, resulting in problems such as small light-emitting area, low brightness, and electrostatic discharge hazard.

In the prior art, by adopting a compatible fabrication process, combined with a high-quality epitaxial process, the generation of low-level defects in the LED chip is reduced, and the LED chip is additionally formed by introducing a diode structure in the process of LED packaging. The surge voltage or pulse current discharge path reduces the harm of static electricity to the LED chip to a certain extent.

However, through the above-mentioned improvement manner, the packaging cost of the LED chip is greatly increased, the implementation difficulty of the process is increased, and the yield of the LED chip is reduced.

Summary of the invention

In order to solve the above problems, the present invention provides an ultraviolet LED flip chip, which has anti-leakage, high luminous efficiency, small voltage surge, anti-static release hazard, heat dissipation. Fast and reliable.

To achieve the above object, the present invention provides the following technical solutions:

An ultraviolet LED flip chip, the ultraviolet LED flip chip comprising:

Substrate

An epitaxial layer structure disposed on the substrate; the epitaxial layer structure includes: a buffer and nucleation layer, a superlattice structure, a heavily doped n-type AlGaN layer, and a lightly doped n sequentially disposed in a first direction Type AlGaN layer, quantum well active region, electron blocking layer, P-type conductive layer, reflective layer, current spreading layer, insulating layer and conductive film layer;

Wherein the first direction is perpendicular to the substrate and directed by the substrate to the epitaxial layer structure.

Preferably, in the above ultraviolet LED flip chip, the insulating layer is disposed in an intermediate portion of the current spreading layer, and the current spreading layer and the insulating layer are respectively in contact with the reflective layer.

Preferably, in the above ultraviolet LED flip chip, the ultraviolet LED flip chip further comprises:

a first through the lightly doped n-type AlGaN layer, the quantum well active region, the electron blocking layer, the P-type conductive layer, the reflective layer, the current spreading layer, and the conductive thin film layer An electrode groove structure;

a second electrode recess structure penetrating the current spreading layer and the conductive thin film layer;

Setting through the lightly doped n-type AlGaN layer, the quantum well active region, the electron blocking layer, the P-type conductive layer, the reflective layer, the insulating layer, and the conductive thin film layer a third groove structure of the shape.

Separating layers disposed on inner sidewalls of the first electrode recess structure and inner sidewalls of the second electrode recess structure;

And an inner contact layer disposed on an inner sidewall of the first electrode recess structure and an inner sidewall of the second electrode recess structure facing away from the side of the isolation layer.

An n-electrode disposed on a surface of the conductive film layer and in contact with the first electrode groove structure;

a p-electrode disposed on a surface of the conductive film layer and in contact with the second electrode groove structure.

a SiO ₂ layer disposed inside the third recess structure, and a thickness of the SiO ₂ layer is smaller than a distance from the heavily doped n-type AlGaN layer to the insulating layer in the first direction ;

a metal ring layer disposed on the SiO ₂ layer, the metal ring layer being an inverted E structure of an unclosed structure for encapsulating an epitaxial layer structure region of the n electrode and not connected to the n electrode .

Preferably, in the above ultraviolet LED flip chip, the ultraviolet LED flip chip further comprises: a substrate structure;

The substrate structure includes: a metal wiring layer, an AlN layer, a conductive silver paste layer, and a substrate which are sequentially disposed in the first direction.

Preferably, in the above ultraviolet LED flip chip, the P-type conductive layer comprises: a P-type AlGaN layer and a P-type GaN layer;

The P-type AlGaN layer and the P-type GaN layer are sequentially disposed between the electron blocking layer and the reflective layer in the first direction.

Preferably, in the above ultraviolet LED flip chip, the heavily doped n-type AlGaN layer has a thickness of 1.7 um to 1.9 um, including an endpoint value.

Preferably, in the above ultraviolet LED flip chip, the lightly doped n-type AlGaN layer has a thickness of 0.1 um to 0.3 um, inclusive.

It can be seen from the above description that the ultraviolet LED flip chip provided by the present invention is arranged in turn by weight The n-type AlGaN layer and the lightly doped n-type AlGaN layer are doped instead of the conventional n-type AlGaN layer having the same thickness, and by optimizing the thickness of the lightly doped n-type AlGaN layer, the epitaxial structure of the LED chip can be directly increased. The equivalent series resistance in one direction makes the current spreading of the LED chip epitaxial structure in the vertical first direction more efficient.

Moreover, an electron blocking layer and a reflective layer are respectively disposed on both sides of the P-type conductive layer, which greatly improves the luminous efficiency of the ultraviolet LED chip.

DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the description of the prior art will be briefly described below. Obviously, the drawings in the following description are only It is a certain embodiment of the present invention, and other drawings can be obtained from those skilled in the art without any creative work.

1 is a schematic cross-sectional view of an ultraviolet LED flip chip according to an embodiment of the present invention;

2 is a top view of an ultraviolet LED flip chip according to an embodiment of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention are clearly and completely described in the following with reference to the accompanying drawings in the embodiments of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, but not all embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without creative efforts are within the scope of the present invention.

The present invention will be further described in detail with reference to the accompanying drawings and specific embodiments.

Referring to FIG. 1, FIG. 1 is a schematic cross-sectional view of an ultraviolet LED flip chip according to an embodiment of the present invention.

In the embodiment of the present invention, as shown in FIG. 1, the ultraviolet LED flip chip includes:

Substrate 1.

An epitaxial layer structure disposed on the substrate 1; the epitaxial layer structure includes: a buffer and nucleation layer 2, a superlattice structure 3, a heavily doped n-type AlGaN layer 4, which are sequentially disposed in a first direction, The n-type AlGaN layer 5, the quantum well active region 6, the electron blocking layer 7, the P-type conductive layer 8, the reflective layer 9, the current spreading layer 10, the insulating layer 11, and the conductive thin film layer 12 are lightly doped.

Wherein the first direction is perpendicular to the substrate 1 and is directed by the substrate 1 to the epitaxial layer structure.

Further, the P-type conductive layer 8 includes a P-type AlGaN layer 81 and a P-type GaN layer 82.

The P-type AlGaN layer 81 and the P-type GaN layer 82 are sequentially disposed between the electron blocking layer 7 and the reflective layer 9 in the first direction.

Specifically, the substrate 1 includes, but is not limited to, a sapphire substrate, because the sapphire substrate has a relatively low reflection coefficient, and a sapphire substrate with a pattern optimization design is used as a template, and a process such as etching and etching is formed to form a A cylindrical image with a hexagonal star in cross section and a non-polar sapphire.

Wherein, the thickness of the substrate 1 may be 150 um, the thickness of the buffering and nucleation layer 2 may be 0.1 um, the thickness of the superlattice structure 3 may be 0.2 um, and the thickness of the heavily doped n-type AlGaN layer 4 The thickness of the lightly doped n-type AlGaN layer 5 may be 0.1 um to 0.3 um, the thickness of the quantum well active region 6 may be 1 um, and the thickness of the electron blocking layer 7 may be selected to be 1.7 um to 1.9 um. 0.1 um, the thickness of the P-type AlGaN layer 81 may be 50 nm, the thickness of the P-type GaN layer 82 may be 0.1 um, the thickness of the reflective layer 9 may be 50 nm, and the thickness of the current-expanding layer 10 may be 0.2 um. The thickness of the insulating layer 11 can be selected to be 0.2 um, and the thickness of the conductive thin film layer 12 can be selected to be 0.1 um.

According to the epitaxial layer structure of the present invention, the insulating layer 11 is disposed in an intermediate portion of the current spreading layer 10, and the current spreading layer 10 and the insulating layer 11 are in contact with the reflective layer 9, respectively. That is, in the first direction, after the current spreading layer 10 is grown, the intermediate region of the current spreading layer 10 is etched until the reflective layer 9 is exposed. The insulating layer 11 is deposited in the etched region.

It should be noted that the insulating layer 11 may or may not be in contact with the current spreading layer 10; and the thickness of the insulating layer 11 and the current spreading layer 10 may be the same or different. A process such as photolithography forms a continuous film structure or a discontinuous film structure, ensuring that the current spreading layer 10 and the insulating layer 11 are on the same surface. The material of the current spreading layer 10 includes, but is not limited to, an ITO material, and the material of the insulating layer 11 includes, but is not limited to, a Si ₃ N ₄ material.

The structure of the current spreading layer 10 and the insulating layer 11 is such that when a voltage is applied to the LED chip, at the position of the n-electrode region, the conductive thin film layer 12 corresponding to the insulating layer 11 is also simultaneously applied with a negative voltage, so that The concentration of local carriers in the epitaxial layer structure of the LED chip located above the insulating layer 11 is enhanced, the current spreading is more uniform, and the luminous efficiency is also greatly improved.

Among them, the specific epitaxial layer structure growth process is as follows:

Before the epitaxial layer of the LED chip is grown by MOCVD equipment, hydrogen gas is charged as a shielding gas into the reflection device, and the substrate 1 is pretreated in a high temperature environment of 1000 ° C to remove the pollutants on the surface of the substrate 1 . The AlN nucleation layer is grown under low temperature conditions, and the temperature in the reactor is rapidly heated to 1200 ° C to grow the AlN buffer layer in a high temperature environment; then the five-period AlN/AlGaN superlattice structure is epitaxially grown on the surface thereof. Wherein, each period of the AlN/AlGaN superlattice structure further comprises an AlN layer having a thickness of 15 nm and an AlGaN layer having a thickness of 25 nm; and sequentially growing the heavily doped n-type AlGaN layer 4 and the lightly doped n-type AlGaN layer 5 Slowly lowering the temperature to 600 ° C, epitaxial growth of 20 cycles of AlGaN quantum well active region 6, wherein each period of the quantum well active region includes a 35 nm thick AlGaN well layer and a 15 nm thickness barrier a layer; continuing to epitaxially grow the electron blocking layer 7, the p-type AlGaN layer 81, the p-type GaN layer 82, and the reflective layer 9; using a magnetron sputtering device, depositing the current spreading layer 10 and the insulating layer 11; and growing the conductive thin film layer 12 again .

Compared with the prior art, the ultraviolet LED flip chip provided by the invention improves the n-type AlGaN layer in the conventional LED epitaxial layer structure, and the specific improvement is as follows:

In the case where the thickness of the n-type AlGaN layer is constant, a heavily doped n-type AlGaN layer 4 having a thickness of 1.8 μm between the superlattice structure 3 and the quantum well active region 6 is further heavily doped n A lightly doped n-type AlGaN layer 5 having a thickness of 0.2 um is grown between the AlGaN layer 4 and the quantum well active region 6; and the carrier concentration in the heavily doped n-type AlGaN layer 4 is as high as 3*10 ¹⁹ At the same time as cm ^-3 , the carrier concentration in the lightly doped n-type AlGaN layer 5 is maintained at the order of about 10 ¹⁷ .

Since the reflection and absorption of light by the material of the LED chip itself are taken into consideration, the thickness of the lightly doped n-type AlGaN layer 5 is optimized and thickened by combining the thickness reduction treatment of the epitaxial layer, which directly increases The equivalent series resistance in the first direction of the LED chip epitaxial layer structure further makes the current spreading of the LED epitaxial layer in the vertical first direction more effective, not only improves the output intensity of the LED chip, but also enhances the LED chip resistance. The ability of electrostatic discharge voltage to strike and resist surge current surge avoids excessive current damage to the pn junction in the LED chip structure.

At the same time, by depositing the reflective layer 9 on the side of the p-type GaN layer 82 facing away from the p-type AlGaN layer 81, and performing special processing such as surface roughening on the reflective layer 9, the light can be reflected to the maximum extent. Output again, effectively improving the reflection of light, and obviously enhances the luminous flux of the LED chip. The material of the reflective layer includes, but is not limited to, a metallic silver or a Ni/Ag/Al alloy material structure.

Based on the above embodiment of the present invention, as shown in FIG. 1, the ultraviolet LED flip chip further includes:

Through the lightly doped n-type AlGaN layer 5, the quantum well active region 6, the electron blocking layer 7, the P-type conductive layer 8, the reflective layer 9, the current spreading layer 10, and The first electrode recess structure of the conductive thin film layer 12 is described.

A second electrode recess structure penetrating the current spreading layer 10 and the conductive thin film layer 12.

It should be noted that, in the embodiment of the present invention, a plurality of first electrode recess structures and second electrode recess structures are disposed, and during the etching process, the etching rate is strictly controlled to ensure only a small portion. Etching is performed to reduce damage of the epitaxial layer light-emitting region by etching, thereby improving the light output intensity of the LED chip.

Further, the ultraviolet LED flip chip further includes: an isolation layer 13 respectively disposed on an inner sidewall of the first electrode recess structure and an inner sidewall of the second electrode recess structure.

The inner contact sidewalls 14 are disposed on an inner sidewall of the first electrode recess structure and an inner sidewall of the second electrode recess structure facing away from the side of the isolation layer.

Specifically, an isolation layer 13 is disposed on the inner sidewall of the first electrode recess structure and the inner sidewall of the second electrode recess structure, and the isolation layer 13 preferably solves the formation of leakage current and prevents the metal electrode from contacting the layer structure. The sidewall surface and the LED chip internal contact layer 14 directly form a short circuit caused by a current loop, wherein the thickness of the isolation layer 13 can be selected to be 10 nm.

And, in the process of forming the inner contact layer 14 on the inner side wall of the first electrode groove structure and the inner side wall of the second electrode groove structure facing away from the isolation layer 13, an optional Ti/Al metal alloy is used. As the electrode contact material, the aluminum of the electrode surface enhances the reflection effect of the light, reduces the absorption of part of the light by the edge of the electrode, and increases the extraction of the edge light of the sapphire substrate.

That is to say, when a large external voltage is applied to the LED chip, the formed large pulse current flows through the epitaxial layer structure of the LED chip, and can also flow through the internal contact layer 14 faster, which is better. The shunting action prevents the epitaxial layer of the LED chip from being affected by large pulse currents.

It should be noted that, in FIG. 1, the isolation layer and the internal contact layer in the second electrode recess structure are not labeled.

Further, the ultraviolet LED flip chip further includes:

An n-electrode 15 disposed on a surface of the conductive film layer 12 and in contact with the first electrode groove structure;

a p-electrode 16 disposed on a surface of the conductive thin film layer 12 and in contact with the second electrode recess structure.

Through the lightly doped n-type AlGaN layer 5, the quantum well active region 6, the electron blocking layer 7, the P-type conductive layer 8, the reflective layer 9, the insulating layer 11, and A third groove structure of a set shape of the conductive film layer 12.

Referring to FIG. 2, FIG. 2 is a top view of an ultraviolet LED flip chip according to an embodiment of the present invention.

In the embodiment of the present invention, the third groove structure of the set shape is an inverted E shape structure, wherein the width of the third groove structure may be 20.2 um.

Further, the ultraviolet LED flip chip further includes:

a SiO ₂ layer 17 disposed inside the third recess structure, and a thickness of the SiO ₂ layer 17 is smaller than the first direction from the heavily doped n-type AlGaN layer 4 to the insulating layer 11 the distance between;

a metal ring layer 18 disposed on the SiO ₂ layer 17, the metal ring layer 18 being an inverted E structure of an unclosed structure for encapsulating an epitaxial layer structure region of the n electrode 15 and The n electrode 15 is not connected.

Optionally, the metal ring layer 18 is located at a center of the SiO ₂ layer 17, and the material may be a Cr/Au material, which is a floating, unclosed ring-shaped expanded layer structure.

As shown in FIG. 2, the metal ring layer 18 surrounds the n-electrode region, and the epitaxial layer structure region of the n-electrode 15 is annularly wrapped and not connected to the n-electrode 15.

Specifically, since the electric field intensity inside the pn junction close to the n-electrode 15 is stronger than that of the other semiconductor regions, by providing such a floating, unclosed metal ring layer structure 18, there is electrostatic induction between the n-electrode 15 and the n-electrode 15 And the charge shielding effect of the metal ring layer 18 effectively reduces the peak electric field intensity near the n-electrode 15pn junction region, increases the electrostatic capacitance in the air, and avoids the sharp increase of the reverse current caused by the electric field strength reaching the maximum, and reduces The damage to the LED chip significantly increases the strength of the antistatic strike of the LED chip.

Based on the above embodiment of the present invention, as shown in FIG. 1, the ultraviolet LED flip chip further includes a passivation layer 19.

The passivation layer 19 surrounds the epitaxial layer structure to reduce the influence of leakage current on the LED chip, and prevent the corrosion of the LED chip by the external environment, and improve the current expansion of the active region in the epitaxial layer of the LED chip. The problem is that the current accumulation effect is reduced and the light output power of the LED chip is improved.

According to the above embodiment of the present invention, as shown in FIG. 1, the ultraviolet LED flip chip further includes: a substrate structure.

Wherein, the substrate structure comprises: a metal wiring layer 20, an AlN layer 21, a conductive silver paste layer 22 and a substrate 23 which are sequentially disposed in the first direction; the thickness of the metal wiring layer 20 may be 20 um, AlN The thickness of the layer 21 may be selected to be 0.5 mm, the thickness of the conductive silver paste layer 22 may be 10 μm, and the thickness of the substrate 23 may be 1 mm.

Specifically, the wafer surface bonding technology is used to perform the processes of solid crystal, reverse soldering, and packaging of the LED chip, and the epitaxial layer structure of the LED chip is flip-chip eutectic soldered through the n-electrode 15 and the p-electrode 16 structure. On the substrate 23 of the wiring layer 20, the preliminary packaging of the LED chip is completed.

Wherein, the substrate 23 is preferably a substrate of SiC material, combined with the high-density metal wiring layer 20, so that the thermal path between the quantum well active region 6 and the substrate 23 in the flip-chip structure of the LED chip is shorter, and the heat dissipation is faster; The intermediate position of the metal wiring layer 20 needs to be etched and broken to divide the p electrode region and the n electrode region to prevent a short circuit phenomenon in the LED chip.

Based on all the above embodiments of the present invention, an ultraviolet LED flip chip provided by the present invention has the advantages of anti-leakage, high luminous efficiency, small voltage surge, anti-static release hazard, fast heat dissipation and high reliability.

The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments are obvious to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but the scope of the invention is to be accorded

Claims

An ultraviolet LED flip chip, characterized in that the ultraviolet LED flip chip comprises:

Substrate

An epitaxial layer structure disposed on the substrate; the epitaxial layer structure includes: a buffer and nucleation layer, a superlattice structure, a heavily doped n-type AlGaN layer, and a lightly doped n sequentially disposed in a first direction Type AlGaN layer, quantum well active region, electron blocking layer, P-type conductive layer, reflective layer, current spreading layer, insulating layer and conductive film layer;

Wherein the first direction is perpendicular to the substrate and directed by the substrate to the epitaxial layer structure.
The ultraviolet LED flip chip according to claim 1, wherein the insulating layer is disposed in an intermediate portion of the current spreading layer, and the current spreading layer and the insulating layer are respectively in contact with the reflective layer.
The ultraviolet LED flip chip according to claim 2, wherein the ultraviolet LED flip chip further comprises:

a first through the lightly doped n-type AlGaN layer, the quantum well active region, the electron blocking layer, the P-type conductive layer, the reflective layer, the current spreading layer, and the conductive thin film layer An electrode groove structure;

a second electrode recess structure penetrating the current spreading layer and the conductive thin film layer;

Setting through the lightly doped n-type AlGaN layer, the quantum well active region, the electron blocking layer, the P-type conductive layer, the reflective layer, the insulating layer, and the conductive thin film layer a third groove structure of the shape.
The ultraviolet LED flip chip according to claim 3, wherein the ultraviolet LED flip chip further comprises:

Separating layers disposed on inner sidewalls of the first electrode recess structure and inner sidewalls of the second electrode recess structure;

And an inner contact layer disposed on an inner sidewall of the first electrode recess structure and an inner sidewall of the second electrode recess structure facing away from the side of the isolation layer.
The ultraviolet LED flip chip according to claim 3, wherein the ultraviolet LED flip chip further comprises:

An n-electrode disposed on a surface of the conductive film layer and in contact with the first electrode groove structure;

a p-electrode disposed on a surface of the conductive film layer and in contact with the second electrode groove structure.
The ultraviolet LED flip chip according to claim 5, wherein the ultraviolet LED flip chip further comprises:

a SiO 2 layer disposed inside the third recess structure, and a thickness of the SiO 2 layer is smaller than a distance from the heavily doped n-type AlGaN layer to the insulating layer in the first direction ;

a metal ring layer disposed on the SiO 2 layer, the metal ring layer being an inverted E structure of an unclosed structure for encapsulating an epitaxial layer structure region of the n electrode and not connected to the n electrode .
The ultraviolet LED flip chip according to claim 5, wherein the ultraviolet LED flip chip further comprises: a substrate structure;

The substrate structure includes: a metal wiring layer, an AlN layer, a conductive silver paste layer, and a substrate which are sequentially disposed in the first direction.
The ultraviolet LED flip chip according to claim 1, wherein the P-type conductive layer comprises: a P-type AlGaN layer and a P-type GaN layer;

The P-type AlGaN layer and the P-type GaN layer are sequentially disposed between the electron blocking layer and the reflective layer in the first direction.
The ultraviolet LED flip chip according to claim 1, wherein the heavily doped n-type AlGaN layer has a thickness of 1.7 um to 1.9 um, inclusive.
The ultraviolet LED flip chip according to claim 1, wherein said light The doped n-type AlGaN layer has a thickness of 0.1 um to 0.3 um, inclusive.