LED chip structure and preparation method

Abstract

The application provides an LED chip structure and a preparation method, and belongs to the chip preparation field.The LED chip structure comprises an LED base layer structure, a conductive column is arranged at a corresponding P / N position of the LED base layer structure, a support layer is arranged between the conductive column and the LED base layer structure, and the height of the support layer is adapted to the size of the conductive column.Because the height of the support layer and the conductive column is controllable, the Micro LED with a smaller size can be prepared by using the preparation method, the support layer can be adapted to become shorter when the LED base layer is smaller, the support layer can be adapted to become longer when the LED base layer is larger, and the process has strong universality.

Description

Technical Field

[0001] This invention relates to the field of chip fabrication technology, and in particular to an LED chip structure and fabrication method. Background Technology

[0002] The fabrication of blue-green LED chips based on GaN on conventional sapphire substrates is a mature industry. White light products are now widely used in white light lighting, high-end automotive lighting and other markets. Their device structures can be roughly divided into upright and flip-chip structures with sapphire substrates, as well as thin-film flip-chips without sapphire. However, the significant feature of these applications is the pursuit of high current density and high brightness.

[0003] In the emerging display industry, products often pursue high definition (i.e., high PPI) while meeting brightness requirements. This inherently requires small pixel pitch and small pixel light source, which leads to the development of mini and Micro LED chips.

[0004] Sapphire substrate LEDs are limited by the difficulty of sapphire processing. The chip thickness is difficult to reduce through grinding. Currently, grinding a 4-inch sapphire chip to 60μm results in scratches from the diamond used in grinding and stress from the processing, which can cause the 4-inch chip to crack. This processing limit restricts the chip's dimensions to 60μm (thickness) * 60μm (width) * 60μm (length).

[0005] 1. If the length and width are smaller than the thickness, it will form an unstable columnar shape, and the chip is prone to tipping over.

[0006] 2. The chip's length and width are smaller than its thickness, making it very difficult to cut and process sapphire crystals.

[0007] 3. After the sapphire substrate is peeled off, the remaining GaN-LED epitaxial layer is about 5μm thick, which reduces its mechanical resistance. Both the length and width must not be less than 20μm, otherwise it is prone to cracking.

[0008] It is known that there is a significant size shift between miniature chips with sapphire substrates and microled chips without sapphire substrates. For silicon wafers, although silicon-based processing is easier than sapphire, silicon is opaque and cannot be used for flip-chip fabrication. This affects the chip's light extraction efficiency (external quantum efficiency) and restricts the use of wire bonding processes instead of gold-tin eutectic bonding, solder paste die bonding, and other similar processes. Summary of the Invention

[0009] In view of the limitations of sapphire, silicon-based mini and micro LEDs mentioned above, the technical problem of the present invention is to provide an LED chip structure and fabrication method, wherein the substrate of this structure can be sapphire, silicon, or other substrates, and can be used to make both mini LED chips and micro LEDs.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] On one hand, the present invention provides an LED chip structure, including an LED base layer structure, characterized in that: a conductive post is provided on the LED base layer structure at the P / N position, a support layer is provided between the conductive post and the LED base layer structure, and the height of the support layer and the conductive post is adapted to the size of the LED base layer structure.

[0012] Specifically, the height of the support layer ranges from 5 to 60 μm.

[0013] In particular, the light-transmitting portion of the LED substrate structure is provided with a roughened N-type GaN layer.

[0014] Specifically, one end of the conductive post is connected to the P / N poles of the LED substrate structure, and a conductive bonding layer is formed at the other end of the conductive post.

[0015] Preferably, the conductive pillar is a copper pillar.

[0016] Preferably, the support layer can be one or a mixture of multiple materials selected from PI photoresist, PBO photoresist, photosensitive dry film, non-photosensitive polyimide, ABF dry film, or resin.

[0017] Specifically, the LED substrate structure consists of, from bottom to top, an N-type GaN layer, a light-emitting layer, an Al GaN thin film layer, a P-type GaN layer, an ITO layer, and a DBR insulating layer.

[0018] On the other hand, the present invention also provides a method for manufacturing an LED chip, comprising the following steps:

[0019] Step 1: Generate an electroplated seed layer and a photoresist layer on the LED substrate;

[0020] Step 2: Through a development process, the photoresist layer is developed to create openings at the P / N pole positions;

[0021] Step 3: Electroplat a Cu column inside the opening;

[0022] Step 4: Electroplating a metal bonding layer on the top of the Cu pillar;

[0023] Step 5: Remove the photoresist layer using a stripping process, and then etch away the exposed seed layer;

[0024] Step Six: Form a support layer at the location of the photoresist layer in Step Five;

[0025] Step 7: Remove the substrate to expose the bottom N-type GaN layer.

[0026] Specifically, the manufacturing method further includes:

[0027] Step 8: Roughen the surface of the exposed N-type GaN layer using photolithography and etching techniques.

[0028] The LED chip structure in this application adopts an upward elevation method to control the chip's center of gravity, preventing the chip from tipping over. It also enables flip-chip bonding. The increased height makes it easier to remove the substrate from the bottom. Not to mention the silicon substrate, even the removal of the sapphire substrate will not cause the chip to break.

[0029] Because the height of the support layer and conductive pillars is controllable by the process, this manufacturing method can produce smaller Micro LEDs. The smaller the LED substrate, the shorter the support layer can be, and vice versa. This process has strong versatility. Attached Figure Description

[0030] The invention, its features, shape, and advantages will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings. Like reference numerals denote like parts throughout the drawings. The drawings are not intentionally drawn to scale; the focus is on illustrating the spirit of the invention.

[0031] Figure 1 This is a diagram illustrating the preparation of a sputtering seed layer in an LED chip fabrication method provided by the present invention.

[0032] Figure 2 This is a fabrication diagram of the photoresist layer formed in an LED chip fabrication method provided by the present invention;

[0033] Figure 3 This is a diagram illustrating the preparation of electroplated Cu pillars and metal bonding layers in an LED chip fabrication method provided by this invention.

[0034] Figure 4 This is a preparation diagram of removing the photoresist layer and the exposed seed layer in an LED chip fabrication method provided by the present invention;

[0035] Figure 5 This is a fabrication pattern of forming a support layer and photolithographically exposing a metal bonding layer in an LED chip fabrication method provided by the present invention;

[0036] Figure 6 This is a diagram illustrating the process of stripping the original substrate in an LED chip fabrication method provided by the present invention.

[0037] Figure 7 This is a preparation diagram of the surface roughening of the N-type GaN layer in an LED chip fabrication method provided by the present invention. Detailed Implementation

[0038] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but these are not intended to limit the scope of the invention.

[0039] The LED chip structure fabricated by the method provided by the present invention includes: an N-type GaN layer, a light-emitting layer, an AlGaN thin film layer, a P-type GaN layer, and an ITO layer arranged sequentially from bottom to top; a first target region and a second target region are disposed on the ITO layer; a first trench is formed in the first target region, the bottom surface of the first trench is located inside the N-type GaN layer, and the opening surface of the first trench is coplanar with the upper surface of the ITO layer; an etching stop layer is disposed at the bottom of the first trench and on the surface of the second target region, and a DBR insulating layer is disposed in the region of the ITO layer without an etching stop layer and in the region of the first trench without an etching stop layer; a second trench is formed by the DBR insulating layer outside the second target region and the etching stop layer on the second target region; a seed layer is also disposed on the first trench and the second trench; a Cu pillar is disposed on the seed layer, and a metal bonding layer is disposed on the Cu pillar; a support layer is disposed in the region of the DBR insulating layer without Cu pillars.

[0040] like Figure 1 As shown, this invention provides a method for fabricating an LED chip. First, one of sapphire, silicon carbide, silicon, gallium nitride, or aluminum nitride is used as the primary substrate. An N-type GaN layer, a light-emitting layer, an AlGaN thin film layer, a P-type GaN layer, and an ITO layer are sequentially fabricated on the primary substrate to form a first structure. A first target region for fabricating a first trench and a second target region for fabricating a second trench are defined on the first structure. The first target region where the N-type GaN layer needs to be exposed is fabricated using photolithography, and then etched down to the N-type GaN layer to form the first trench. An etching stop layer is fabricated in the first trench and the second target region. A DBR insulating layer is grown. The bottom of the first trench and the second target region where the etching stop layer needs to be exposed are fabricated using photolithography, and then etched down to the etching stop layer in the first trench and in the second target region to the etching stop layer to create the second trench, thus forming the second structure.

[0041] Then, Ti and Cu seed layers are sputtered onto the second structure, such as Figure 1 As shown; a photoresist layer is formed on the seed layer, such as Figure 2 As shown; next, the photoresist layer is exposed and developed with a developer. The photoresist above the first trench is etched to form the first opening, and the photoresist above the second trench is etched to form the second opening; wherein, the width of the first opening is greater than the width of the first trench, and the width of the second opening is greater than the width of the second trench; 5-60 μm Cu pillars are electroplated on the seed layers of the first and second openings, and a metal bonding layer is electroplated on the Cu pillars, such as... Figure 3 As shown.

[0042] Then, the photoresist layer and the exposed seed layer are removed sequentially to form the third structure, such as... Figure 4 As shown; a PI adhesive or a photosensitive dry film is uniformly applied to the third structure to form a support layer. Photolithography is then performed on the support layer above the metal bonding layer until the metal bonding layer is exposed, as shown. Figure 5 As shown. If PI adhesive is used, it can be cured at high temperature, which can make the adhesive film more stable. In addition, non-photosensitive materials such as polyimide, resin liquid, or ABF dry film can be directly laminated on the third structure to form a support layer. PI adhesive and dry film have good fluidity, which can completely fill the gaps between chips, improving the product reliability of the chip; the cured PI adhesive / dry film also has good support, ensuring the subsequent process transfer, absorption, and welding of LED chips; the thickness of PI adhesive / dry film is selective and controllable, and the patterning accuracy is relatively high, allowing the thickness of LED chips to be developed in the direction of thinner and smaller dimensions. Finally, the original substrate is peeled off, such as Figure 6 As shown, the exposed N-type GaN layer is then roughened using photolithography and etching techniques, such as... Figure 7 As shown, this is done to maximize light extraction efficiency.

[0043] In summary, the fabrication method provided by this invention combines the advantages of direct eutectic bonding between the PN junction of the flip-chip and the positive and negative electrodes on the substrate, avoiding stress damage to the active layer that may be caused during the fabrication and packaging process, and the controllable thickness of the support layer, which allows the chip to be made smaller and thinner as needed.

[0044] The LED chip structure in this application increases the chip's mechanical resistance by adding a support layer. The height of the support layer controls the chip's center of gravity, preventing the chip from tipping over. It also enables flip-chip bonding. The increased height makes it easier to remove the substrate from the bottom. The chemical etching of the silicon substrate is mature and relatively simple. The sapphire substrate is also buffered by the support layer, thereby improving the chip removal yield.

[0045] Because the height of the support layer and conductive pillars is controllable by the process, this manufacturing method can produce smaller Micro LEDs. The smaller the LED substrate, the shorter the support layer can be, and vice versa. This process has strong versatility.

[0046] The preferred embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above. The devices and structures not described in detail should be understood as being implemented in a conventional manner in the art. Any person skilled in the art can make many possible changes and modifications, or equivalent changes to equivalent embodiments without departing from the technical solution of the present invention. This does not affect the substantive content of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the protection scope of the technical solution of the present invention.

Claims

1. An LED chip structure comprising an LED base structure, characterized by: The LED base structure is provided with a conductive column corresponding to the P / N position, and a support layer is arranged between the conductive column and the LED base structure; The LED base structure is composed of an N-type GaN layer, a light-emitting layer, an Al GaN thin film layer, a P-type GaN layer, an ITO layer and a DBR insulating layer from bottom to top; The LED base structure is provided with a first groove and a second groove, the first groove extends downward from the upper surface of the ITO layer to the inside of the N-type GaN layer, and the second groove extends downward from the upper surface of the DBR insulating layer to the etching stop layer, and the DBR insulating layer covers the upper surface of the ITO layer and the inner side wall of the first groove; The conductive column is arranged in the first groove and the second groove, respectively, and the two conductive columns extend upward from the bottom of the first groove and the second groove to the support layer, and the height of the support layer and the conductive column is adapted to the size of the LED base structure: the smaller the LED base structure, the shorter the support layer, and vice versa, the larger the LED base structure, the longer the support layer, the height of the support layer controls the gravity center of the LED chip, and the height range of the support layer and the conductive column is 5-60μm; The light-transmitting part of the LED base structure is provided with a surface-roughened N-type GaN layer; The manufacturing steps of the LED chip structure are as follows: Step one: generate an electroplating seed layer and a photoresist layer on the LED base structure on the substrate; Before generating the electroplating seed layer and the photoresist layer, the LED base structure is prepared on the substrate, and the LED base structure includes an N-type GaN layer, a light-emitting layer, an Al GaN thin film layer, a P-type GaN layer, and an ITO layer; The ITO layer is provided with a first target area and a second target area, the first target area is a N electrode corresponding area, and the second target area is a P electrode corresponding area; A first groove is opened in the first target area to expose the N-type GaN layer corresponding to the first target area; An etching stop layer is prepared at the bottom of the first groove and the second target area; A DBR insulating layer is grown, and the DBR insulating layer covers the inside of the first groove, the surface of the stop layer, and the exposed surface of the ITO layer; Etching the DBR insulating layer: etching to the etching stop layer in the first groove, and etching to the etching stop layer in the second target area to form a second groove; The seed layer is generated on the exposed surface of the DBR insulating layer and the surface of the etching stop layer; The photoresist layer is coated on the surface of the seed layer to form the photoresist layer; Step two: develop the photoresist layer to open an opening at the P / N electrode position through a developing process, including a first opening and a second opening, the width of the first opening is greater than the width of the first groove, and the width of the second opening is greater than the width of the second groove; Step three: electroplate a copper column in the opening; Step four: electroplate a metal bonding layer on the top of the copper column; Step five: remove the photoresist layer by a gel removing process, and then etch to remove the exposed seed layer; Step six: form a support layer at the position of the photoresist layer in step five, and perform photoetching on the support layer on the metal bonding layer until the metal bonding layer is exposed. Step seven: removing the substrate to expose the bottom N-type GaN layer; Step eight: roughening the exposed N-type GaN layer by photolithography and etching technology.

2. The LED chip structure of claim 1, wherein, One end of the conductive column is connected with the P / N pole of the LED base layer structure, and the other end of the conductive column is formed with a conductive bonding layer.

3. The LED chip structure of claim 2, wherein, The conductive column is a copper column.

4. The LED chip structure of claim 1, wherein, The support layer is one or a mixture of multiple materials of PI photoresist, PBO photoresist, photosensitive dry film, non-photosensitive polyimide, ABF dry film or resin.

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