CN104134723A - Vertical type LED chip structure and manufacturing method thereof - Google Patents

Abstract

The present invention proposes a vertical LED chip structure and a preparation method thereof, in which a transparent conductive contact layer, a low-refractive index medium layer with distribution patterns and a reflective layer are sequentially formed on the P-GaN layer to form a composite reflector composed of three layers, The low refractive index medium layer can occupy a large area of the composite mirror, which can greatly reduce the light absorption ratio of the mirror, and because the transparent conductive contact layer has excellent lateral conductivity, it can ensure the uniform distribution of current in the entire P-GaN layer , effectively improving the comprehensive effective reflectivity of the composite mirror.

Description

Vertical LED chip structure and preparation method thereof

technical field

The invention relates to the field of LED chip manufacturing, in particular to a vertical LED chip structure and a preparation method thereof.

Background technique

In recent years, research on light-emitting diodes (Light-Emitting Diode, LED) has become a trend. LED chips have two basic structures: lateral structure (Lateral) and vertical structure (Vertical). The traditional positive structure LED chip is a typical representative of the lateral structure. The LED chip is formed on the sapphire substrate. Due to the limitation of the non-conductive and poor thermal conductivity of the sapphire substrate, the lateral structure has inherent defects since its birth: (1) The sapphire is not conductive, and the P electrode and the N electrode are both on the LED chip. On the same side of the N-type confinement layer, this brings many unfavorable factors, such as 1. In terms of electrical performance, the current crowding effect (Current crowding) caused by the unequal distance of the current flowing laterally in the n- and p-type confinement layers; 2. The light output In terms of performance, both the N electrode and the P electrode are on the light-emitting surface to cause electrode shading problems; (2) The thermal conductivity of sapphire is very poor, and the PN junction heat of the lateral structure LED chip needs to be exported through the sapphire substrate. For the chip, the heat conduction path is longer, and the thermal resistance of this LED chip is relatively large, and the working current is also limited.

In order to overcome these deficiencies of the horizontal structure LED chips, Cree Company of the United States, Osram Company of Germany, Philips Lumileds Company of the United States and SemiLEDs of the United States are actively developing vertical LED chips (hereinafter referred to as V-LEDs). V-LEDs use silicon or metal substrates with high conductivity and good heat dissipation. On the one hand: the P electrode and N electrode of the V-LED chip are respectively on both sides of the epitaxial layer of the LED chip. Since the patterned electrode and all the p-type confinement layers are used as the P surface electrode, the current almost flows through the LED chip vertically. The epitaxial layer, with very little lateral flow of current, can improve the current distribution of the planar structure, improve the luminous efficiency, and can also solve the shading problem of the P electrode, and increase the light-emitting area of the LED chip; on the other hand: the substrate adopts a good thermal conductivity Silicon or metal, PN junction heat dissipation problems can be solved, and large-size power chips can be realized.

Since the silicon or metal substrate in contact with the P electrode at the bottom cannot transmit light, a reflector will be formed on the P surface of the V-LED chip to increase the light extraction efficiency. The V-LED chip mainly emits light from the top N surface, and the P surface The quality of the ohmic contact and the reflectivity of the mirror become the key points for the success of the V-LED chip, and the reflectivity of the P surface mirror directly determines the luminous brightness of the V-LED chip. At present, the light reflectors used in vertical LED chips are mainly metal structures, relying on the high reflectivity of Ag, Al, Rh and other metals to complete the reflection of light from the light to the bottom of the chip.

Please refer to FIG. 1. FIG. 1 is a schematic structural diagram of a vertical LED chip in the prior art. At present, V-LED chips on the market include a substrate 10, a protective layer and a metal bonding layer sequentially formed on the substrate 10. 20. Mirror 30, P-GaN layer 40, quantum well layer 50, N-GaN layer 60 and N electrode 70. Generally, the reflective mirror 30 is mostly made of metal material with high reflectivity, and Ag is commonly used as the main reflective material. Due to the active nature of Ag, the formed reflector 30 is prone to oxidation, clustering, migration and other phenomena, so a protective layer needs to be prepared; due to the poor adhesion between Ag and the P-GaN of the V-LED chip, the front of the reflector 30 Usually a layer of Cr, Ni (not shown) and other metals are prepared to solve the adhesion problem. However, the interface of the reflector 30 formed solely of Ag or other metal materials will absorb light to a certain extent, reducing the efficiency of light emission.

In order to solve the above problems, a vertical LED chip structure as shown in Figure 2 is also proposed in the prior art. According to the physical phenomenon of total reflection of visible light from an optically denser medium to an optically rarer medium, the reflection of the Ag material The double-layer composite mirror composed of the mirror 30 and a layer of non-conductive low-refractive index medium (such as SiO ₂ ) can effectively reduce light absorption at the interface of the mirror 30 and improve the effective reflectivity of the composite mirror. As shown in FIG. 2, the vertical LED chip proposed in FIG. 2 is similar to that in FIG. Reflectivity.

Another important function of the composite reflector is to serve as an ohmic contact layer on the P side of the vertical LED chip, and the low-refractive index medium 31 (usually SiO ₂ ) is not conductive, so it cannot realize the function of ohmic contact, so it can only be made of Ag material. Therefore, it is necessary to ensure that the reflector 30 of Ag material accounts for a considerable proportion in the compound reflector, and the surface area occupied by the low-refractive index medium 31 in the compound reflector only accounts for 20% of the surface area of the compound reflector. -80%, but the reflectivity of the composite mirror cannot be increased by infinitely increasing the proportion of the low-refractive index medium 31 in the composite mirror. In addition, the lateral current spreading ability of the P surface is extremely weak, and this mirror relying on Ag material 30 distribution to adjust the current distribution of the double-layer composite mirror is difficult to spread the current uniformly to the entire P surface.

Therefore, how to solve the problems existing in the reflectors in the prior art has become an important task for those skilled in the art.

Contents of the invention

The purpose of the present invention is to provide a vertical LED chip structure and a preparation method thereof, which can reduce the light absorption ratio of the reflector while taking into account the uniform distribution of current on the P surface of the vertical LED chip.

In order to achieve the above object, the present invention proposes a method for preparing a vertical LED chip structure, comprising steps:

A growth substrate is provided, and an epitaxial layer is formed on the growth substrate, the epitaxial layer includes an undoped layer, an N-GaN layer, a quantum well layer and a P-GaN layer formed in sequence, and the undoped layer is formed on said growth substrate;

forming a transparent conductive contact layer on the P-GaN layer;

forming a low-refractive index medium layer on the transparent conductive contact layer, performing photolithography on the low-refractive index medium layer, and etching a distribution pattern, and the distribution pattern exposes the transparent conductive contact layer;

forming a reflective layer on the low refractive index medium layer and the transparent conductive contact layer;

forming a protective layer and a metal bonding layer on the reflective layer;

bonding a bonding substrate on the metal bonding layer;

removing the growth substrate, and etching the undoped layer to expose the N-GaN layer;

An N electrode is formed on the N-GaN layer.

Further, in the preparation method of the vertical LED chip structure, the material of the transparent conductive contact layer is ITO, ZnO or AZO.

Further, in the preparation method of the vertical LED chip structure, the material of the low refractive index medium layer is one or more of SiO ₂ , SiN _x , Ti ₃ O ₅ , Al ₂ O ₃ stacked and In this way, the thickness of the low refractive index medium layer is in the range of 10 angstroms to 50 μm.

Further, in the preparation method of the vertical LED chip structure, the area of the low refractive index medium layer accounts for 85%-95% of the area of the vertical LED chip.

Further, in the preparation method of the vertical LED chip structure, a reflective layer is evaporated and formed in a fixed area by negative adhesive stripping technology, so that the size of the reflective layer is smaller than that of the vertical LED chip.

Further, in the method for preparing the vertical LED chip structure, the reflective layer is made of Ag, Al or Rh.

Further, in the preparation method of the vertical LED chip structure, the protective layer is made of (Ti-Pt)x or TiW-Pt combination, and the metal bonding layer is made of Au, Sn or AuSn alloy.

Further, in the method for preparing the vertical LED chip structure, the bonding substrate is made of Si, Cu or MoCu.

Further, in the preparation method of the vertical LED chip structure, the growth substrate is removed by laser lift-off or chemical lift-off.

Further, in the preparation method of the vertical LED chip structure, after removing the growth substrate and before forming the N electrode, the undoped layer is firstly etched by wet or dry etching , exposing the N-GaN layer; secondly, performing roughening treatment on the N-GaN layer to form a rough surface, and the solution used for the roughening treatment is KOH or H ₂ SO ₄ .

Further, in the method for preparing the vertical LED chip structure, after the N electrode, a passivation layer is formed on the rough surface, and the passivation layer is SiO ₂ .

Further, in the preparation method of the vertical LED chip structure, the material of the N electrode is Ni/Au, Al/Ti/Pt/Au or Cr/Pt/Au.

The present invention also proposes a vertical LED chip structure, which is formed by the method for preparing the vertical LED chip structure as described above, and the structure includes in sequence: a bonding substrate, a metal bonding layer, a protective layer, and a reflective layer . A low-refractive-index medium layer with a distribution pattern, a transparent conductive contact layer, a P-GaN layer, a quantum well layer, an N-GaN layer and an N electrode, wherein the N electrode is connected to the N-GaN layer.

Further, in the vertical LED chip structure, it also includes a rough surface and a passivation layer, the rough surface is formed on the surface of the N-GaN layer, the passivation layer is formed on the rough surface, Both the rough surface and the passivation layer expose the N electrode.

Compared with the prior art, the beneficial effect of the present invention is mainly reflected in: a composite reflector composed of a transparent conductive contact layer, a low-refractive index medium layer with a distribution pattern and a reflective layer is sequentially formed on the P-GaN layer, The low refractive index medium layer can occupy a large area of the composite mirror, which can greatly reduce the light absorption ratio of the mirror, and because the transparent conductive contact layer has excellent lateral conductivity, it can ensure the uniform distribution of current in the entire P-GaN layer , effectively improving the comprehensive effective reflectivity of the composite mirror.

Description of drawings

FIG. 1 is a schematic structural view of a vertical LED chip in the prior art;

FIG. 2 is a schematic structural diagram of another vertical LED chip in the prior art;

3 is a flowchart of a method for preparing a vertical LED chip structure in an embodiment of the present invention;

4 to 12 are schematic cross-sectional views during the fabrication process of the vertical LED chip structure in an embodiment of the present invention.

Detailed ways

The vertical LED chip structure of the present invention and its preparation method will be described in more detail below in conjunction with schematic diagrams, wherein a preferred embodiment of the present invention is shown, and it should be understood that those skilled in the art can modify the present invention described here and still realize Advantageous effects of the present invention. Therefore, the following description should be understood as the broad knowledge of those skilled in the art, but not as a limitation of the present invention.

In the interest of clarity, not all features of an actual implementation are described. In the following description, well-known functions and constructions are not described in detail since they would obscure the invention with unnecessary detail. It should be appreciated that in the development of any actual embodiment, numerous implementation details must be worked out to achieve the developer's specific goals, such as changing from one embodiment to another in accordance with system-related or business-related constraints. Additionally, it should be recognized that such a development effort might be complex and time consuming, but would nevertheless be merely a routine undertaking for those skilled in the art.

In the following paragraphs the invention is described more specifically by way of example with reference to the accompanying drawings. Advantages and features of the present invention will be apparent from the following description and claims. It should be noted that all the drawings are in a very simplified form and use imprecise scales, and are only used to facilitate and clearly assist the purpose of illustrating the embodiments of the present invention.

Please refer to FIG. 3. In this embodiment, a method for preparing a vertical LED chip structure is proposed, including steps:

S100: Provide a growth substrate, and form an epitaxial layer on the growth substrate, the epitaxial layer includes an undoped layer, an N-GaN layer, a quantum well layer, and a P-GaN layer that are sequentially formed, the undoped a layer is formed on the growth substrate;

S200: forming a transparent conductive contact layer on the P-GaN layer;

S300: forming a low-refractive-index medium layer on the transparent conductive contact layer, performing photolithography on the low-refractive-index medium layer, and etching a distribution pattern, the distribution pattern exposing the transparent conductive contact layer;

S400: forming a reflective layer on the low refractive index medium layer and the transparent conductive contact layer;

S500: forming a protective layer and a metal bonding layer on the reflective layer;

S600: bonding a bonding substrate on the metal bonding layer;

S700: removing the growth substrate, and etching the undoped layer, exposing the N-GaN layer;

S800: forming an N electrode on the N-GaN layer.

Specifically, referring to FIG. 4 , in step S100 , a growth substrate 100 is provided, and the growth substrate 100 may be a sapphire substrate, a silicon substrate, a SiC substrate, a patterned substrate, and the like. In this embodiment, the epitaxial layer includes an undoped layer 210, an N-GaN layer 220, a quantum well layer 230, and a P-GaN layer 240, wherein the epitaxial layer can be deposited by MOCVD (Metal Organic Chemical VaporDeposition) and/or MBE (Molecular Beam Epitaxy) and other growth methods.

Please refer to FIG. 5, in step S200, a transparent conductive contact layer 300 is formed on the P-GaN layer 240, and the material of the transparent conductive contact layer 300 is a low-resistance high-transmittance film such as ITO, ZnO or AZO, The transparent conductive contact layer 300 is used as an ohmic contact layer.

Please refer to FIG. 6, in step S300, a low-refractive-index medium layer 400 is formed on the transparent conductive contact layer 300, and the low-refractive-index medium layer 400 is provided with distribution patterns, that is, through holes 410 are formed, and the distribution pattern The pattern exposes the transparent conductive contact layer 300 , and the distribution pattern can be of various properties, such as a circle, a square, or a distribution of different combinations of patterns, etc., which are not limited here. The material of the low refractive index medium layer 400 is stacked by one or more of SiO ₂ , SiN _x , Ti ₃ O ₅ , Al ₂ O ₃ , and the thickness range of the low refractive index medium layer 400 is 10 Angstroms. ~50 μm, eg 100 angstroms. The low refractive index dielectric layer 400 can be formed by electron beam (E-beam), sputtering (Sputter), reactive plasma deposition (Reactive Plasma Deposition, RPD), etc., preferably, the formed low refractive index dielectric layer The area of 400 accounts for 85% to 95% of the area of the vertical LED chip, thereby greatly reducing the proportion of light absorbed by the subsequently formed reflector.

Please refer to FIG. 7, in step S400, a reflective layer 500 is formed on the low-refractive index medium layer 400 and the exposed transparent conductive contact layer 300, specifically, a lift-off technique is used in the fixed area The reflective layer 500 is formed by vapor deposition, so that the size of the reflective layer 500 is smaller than the size of the vertical LED chip, even if the reflective layer 500 exposes the edge of the vertical LED chip, it is convenient for the subsequent formation of a protective layer to cover all the vertical LED chips. The reflective layer 500 is used for protection. The reflective layer 500 is made of Ag, Al or Rh.

Please refer to FIG. 8, in step S500, a protective layer and a metal bonding layer 600 are formed on the reflective layer 500 (in order to simplify the drawings, the protective layer and the metal bonding layer are shown as one layer), the The protective layer is made of (Ti-Pt) _x or TiW-Pt combination, and the protective layer fully covers the reflective layer 500 to protect it. The material of the metal bonding layer is Au, Sn or AuSn alloy, which is used for bonding with the subsequently formed bonding substrate.

Referring to FIG. 9 , in step S600 , a bonding substrate 700 is bonded on the metal bonding layer; the bonding substrate 700 is made of a conductive substrate such as Si, Cu or MoCu with good heat dissipation.

Please refer to FIG. 10 , in step S700 , the growth substrate 100 is removed, and the growth substrate 100 can usually be removed by laser lift-off or chemical lift-off. Usually, a layer of metal Ga is formed on the surface of the undoped layer 210 by laser lift-off. Therefore, it is necessary to use acid or alkali to remove metal Ga, and the solution used may be HCL or KOH.

Please refer to FIG. 11 , before forming the N electrode, the undoped layer 210 is first etched by wet or dry (ICP) etching to expose the N-GaN layer 220, wherein the The undoped layer 210 can be completely etched and removed, or only part of it can be removed; secondly, the N-GaN layer 220 is roughened to form a rough surface 211, and the rough surface 211 formed by the roughening treatment can increase the N-GaN layer The surface area of 220 increases the light emitting area and improves the luminous efficiency.

Please refer to FIG. 12. In step S800, an N electrode 212 is formed on the N-GaN layer 220. The material of the N electrode 212 is Ni/Au, Al/Ti/Pt/Au or Cr/Pt/Au. After the N electrode 212 , a passivation layer 800 is formed on the rough surface 211 . The passivation layer 800 is SiO ₂ for protecting the entire chip. The formed passivation layer 800 exposes the N electrode 212 .

Please continue to refer to FIG. 12. On the other side of the present invention, a vertical LED chip structure is also proposed, which is formed by the above-mentioned vertical LED chip structure preparation method, and the structure includes in turn: a bonding substrate 700, protective layer and metal bonding layer 600, reflective layer 500, low refractive index medium layer 400 with distribution pattern, transparent conductive contact layer 300, P-GaN layer 240, quantum well layer 230, N-GaN layer 220, The N electrode 212, the rough surface 211 and the passivation layer 800, wherein the N electrode 212 is connected to the N-GaN layer 220, the rough surface 211 is formed on the surface of the N-GaN layer 220, and the passivation A layer 800 is formed on the rough surface 211 , and both the rough surface 211 and the passivation layer 800 expose the N electrode 212 .

To sum up, in the vertical LED chip structure and its preparation method provided by the embodiment of the present invention, a transparent conductive contact layer, a low-refractive index medium layer with a distribution pattern, and a reflective layer are sequentially formed on the P-GaN layer. The composite mirror can make the low refractive index medium layer occupy a larger area of the composite mirror, which can greatly reduce the light absorption ratio of the mirror, and because the transparent conductive contact layer has excellent lateral conductivity, it can ensure that the current is in the entire P- The uniform distribution of the GaN layer effectively improves the comprehensive effective reflectivity of the composite mirror.

The foregoing are only preferred embodiments of the present invention, and do not limit the present invention in any way. Any person skilled in the technical field, within the scope of the technical solution of the present invention, makes any form of equivalent replacement or modification to the technical solution and technical content disclosed in the present invention, which does not depart from the technical solution of the present invention. The content still belongs to the protection scope of the present invention.

Claims (14)

1. a preparation method for vertical-type LED chip structure, is characterized in that, comprises step:

Growth substrates is provided, in described growth substrates, forms epitaxial loayer, described epitaxial loayer comprises the undoped layer, N-GaN layer, quantum well layer and the P-GaN layer that form successively, and described undoped layer is formed in described growth substrates;

On described P-GaN layer, form electrically conducting transparent contact layer;

On described electrically conducting transparent contact layer, form low refractive index dielectric layer, described low refractive index dielectric layer is carried out to photoetching, etch distribution pattern, described distribution pattern exposes described electrically conducting transparent contact layer;

On described low refractive index dielectric layer and electrically conducting transparent contact layer, form reflector;

On described reflector, form protective layer and metal bonding layer;

Bonding bonded substrate on described metal bonding layer;

Remove described growth substrates, and undoped layer described in etching, described N-GaN layer exposed;

On described N-GaN layer, form N electrode.

2. the preparation method of vertical-type LED chip structure as claimed in claim 1, is characterized in that, described electrically conducting transparent contact layer material is ITO, ZnO or AZO.

3. the preparation method of vertical-type LED chip structure as claimed in claim 1, is characterized in that, described low refractive index dielectric layer material is SiO ₂, SiN _x, Ti ₃o ₅, Al ₂o ₃in one or more stacking forming, the thickness range of described low refractive index dielectric layer is 10 dust～50 μ m.

4. the preparation method of vertical-type LED chip structure as claimed in claim 1, is characterized in that, the area of described low refractive index dielectric layer accounts for 85%～95% of described vertical-type LED chip area.

5. the preparation method of vertical-type LED chip structure as claimed in claim 1, is characterized in that, adopts negative glue lift-off technology to form reflector at fixed area evaporation, makes the size in described reflector be less than the size of described vertical-type LED chip.

6. the preparation method of vertical-type LED chip structure as claimed in claim 5, is characterized in that, the material in described reflector is Ag, Al or Rh.

7. the preparation method of vertical-type LED chip structure as claimed in claim 1, is characterized in that, described protective layer material is (Ti-Pt) x or TiW-Pt combination, and described metal bonding layer material is Au, Sn or AuSn alloy.

8. the preparation method of vertical-type LED chip structure as claimed in claim 1, is characterized in that, described bonded substrate material is Si, Cu or MoCu.

9. the preparation method of vertical-type LED chip structure as claimed in claim 1, is characterized in that, adopts laser lift-off or chemical stripping to remove described growth substrates.

10. the preparation method of vertical-type LED chip structure as claimed in claim 1, it is characterized in that, after removing described growth substrates, before forming described N electrode, first adopt wet method or dry etching to carry out etching to undoped layer, expose described N-GaN layer; Secondly described N-GaN layer is carried out to roughening treatment and form matsurface, it is KOH or H that described roughening treatment is used solution ₂sO ₄.

The preparation method of 11. vertical-type LED chip structures as claimed in claim 10, is characterized in that, after described N electrode, on described matsurface, forms passivation layer, and described passivation layer is SiO ₂.

The preparation method of 12. vertical-type LED chip structures as claimed in claim 1, is characterized in that, described N electrode material is Ni/Au, Al/Ti/Pt/Au or Cr/Pt/Au.

13. 1 kinds of vertical-type LED chip structures; adopt and form as the preparation method of the vertical-type LED chip structure as described in any one in claim 1 to 13; it is characterized in that; described structure comprises successively: bonded substrate, metal bonding layer, protective layer, reflector, the low refractive index dielectric layer that is provided with distribution pattern, electrically conducting transparent contact layer, P-GaN layer, quantum well layer, N-GaN layer and N electrode; wherein, described N electrode is connected with described N-GaN layer.

14. vertical-type LED chip structures as claimed in claim 13, it is characterized in that, also comprise matsurface and passivation layer, described matsurface is formed at described N-GaN layer surface, described passivation layer is formed on described matsurface, and described matsurface and passivation layer all expose described N electrode.