Micro light emitting diode display chip and preparation method

Abstract

The application discloses a micro light emitting diode display chip and a preparation method thereof, and belongs to the technical field of semiconductor devices. The preparation method comprises the following steps: providing a substrate with contacts; providing a substrate with an LED epitaxial layer; providing a mirror, which is arranged on the LED epitaxial layer; patterning the mirror to form a reflection unit; and providing LED pixel points, wherein the contacts are located between adjacent LED pixel points. The display chip comprises a substrate, LED pixel points, a bonding layer and a reflection unit, and the LED pixel points are individually driven through the substrate. The application adopts a vertical structure, the reflection unit is only located below the LED pixel points, the mirror is patterned, the probability that an etching solution contacts the reflection unit during removal of a wet mask is reduced, the influence of wet processing on the mirror can be greatly reduced, the conductivity and adhesion of the LED pixel points are improved, and the influence of mirror sputtering on the device is avoided in the pixel isolation process.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device technology, specifically relating to a miniature light-emitting diode display chip and its fabrication method. Background Technology

[0002] Micro-LED, also known as micro light-emitting diode, is a micro LED array with multiple single-pixel elements. The distance between the LED pixels in the array is on the order of 100 nanometers to 100 micrometers, and each LED pixel can emit light on its own.

[0003] In the Micro-LED manufacturing process, in order to increase the light extraction efficiency of LEDs, a reflector layer needs to be added to improve reflectivity. The known reflector is a metal structure that is vapor-deposited on the entire surface. However, the following problems exist in the actual process: (1) Due to defects in the epitaxial wafer, after the LED pixel is formed, the mask needs to be removed by wet etching. However, the etching solution will seep into the reflector through the defects and corrode the metal structure of the reflector, making this part of the area unusable, producing bulges, and affecting the conductivity and adhesion of the LED pixel; (2) Since the traditional reflector is vapor-deposited before the LED pixel isolation process, the reflector will be etched at the same time when the LED pixel is formed, resulting in metal sputtering of the reflector. Since the metal is relatively active, it will cover the etched groove and the area around the etched area to varying degrees, causing short circuits and leakage. Summary of the Invention

[0004] Objective of the Invention: The objective of this invention is to provide a miniature light-emitting diode (LED) display chip that improves the light extraction efficiency of LED pixels by adding a reflector to the epitaxial layer. Another objective of this invention is to provide a method for fabricating the aforementioned miniature LED display chip, which reduces the impact of wet etching on the reflector metal by patterning the reflector, and avoids the impact of reflector metal sputtering on the device during the LED pixel isolation process.

[0005] Technical solution: To achieve the above-mentioned objective, a method for fabricating a micro light-emitting diode display chip includes:

[0006] Provide substrate;

[0007] An LED epitaxial layer is provided, wherein the LED epitaxial layer is disposed on a substrate;

[0008] A reflector is formed on the LED epitaxial layer;

[0009] The reflector is patterned to form multiple reflective units arranged in an array;

[0010] A bonding layer is formed on the substrate and / or the LED epitaxial layer, the bonding layer covering the reflective unit, thereby bonding the substrate and the LED epitaxial layer;

[0011] Remove the substrate;

[0012] Multiple LED pixels are arranged in an array on the LED epitaxial layer; the reflective unit is located between the corresponding LED pixel and the bonding layer.

[0013] In some embodiments, an LED epitaxial layer is provided on the substrate, and the epitaxial process can be completed by MOCVD technology. The substrate can be selected as sapphire, silicon or gallium nitride; the LED epitaxial layer includes an n-type semiconductor layer and a p-type semiconductor layer.

[0014] In some embodiments, the substrate can be removed by dry etching, wet etching, mechanical polishing, or laser lift-off.

[0015] In some embodiments, the LED epitaxial layer includes a first doped semiconductor layer, a second doped semiconductor layer, and an active layer located between the two; the first doped semiconductor layer is a continuous functional layer structure, and the second doped semiconductor layer is etched to form a mesa structure to form the LED pixels arranged in an array.

[0016] In some embodiments, the second doped semiconductor layer can be ion implanted to form the LED pixels arranged in an array.

[0017] In some embodiments, the step of etching the second doped semiconductor layer to form a mesa structure includes:

[0018] A patterned mask is formed on the second doped semiconductor layer;

[0019] The region on the second doped semiconductor layer not covered by the mask is etched, and the etching depth is at least the depth of the second doped semiconductor layer;

[0020] Remove the mask to form the mezzanine structure.

[0021] In some embodiments, etching to form a mesa structure may include dry etching or wet etching processes.

[0022] In some embodiments, a mask is required in the etching process to form the mesa structure. After the mesa structure is formed, the mask formed on the second doped semiconductor layer needs to be removed. The removal methods include wet etching.

[0023] In some embodiments, the mesa structure formed by etching the LED epitaxial layer includes dry etching or wet etching, and the formed mesa structure can be a vertical sidewall structure or a trapezoidal structure.

[0024] In some embodiments, the substrate includes a driving circuit and a plurality of contacts connected to the driving circuit, the contacts being located between adjacent LED pixels; the LED pixels are electrically connected to the corresponding contacts, such that the LED pixels can be independently driven by the corresponding contacts.

[0025] In some embodiments, the electrical connection between the LED pixel and the corresponding contact specifically refers to the formation of an electrical connection structure between the LED pixel and the corresponding contact, enabling the contact to independently drive the corresponding LED pixel.

[0026] In some embodiments, the LED pixels are miniature light-emitting diodes, and the LED pixels are arranged in an array; the light emitted by the pixels is any one of red light, green light, blue light, yellow light or ultraviolet light; the reflective units are arranged in an array, and the reflective units are configured in a one-to-one correspondence with the LED pixels.

[0027] In some embodiments, the step of patterning the reflector to form a reflective unit, and patterning the reflector to form a plurality of reflective units arranged in an array, and bonding the substrate to the LED epitaxial layer includes:

[0028] A photoresist layer is formed on the reflector by photolithography;

[0029] The reflective unit is formed by patterning the mirror using dry etching and then removing the photoresist layer.

[0030] Align the reflective unit with the LED pixel to bond the substrate to the LED epitaxial layer.

[0031] In some embodiments, the step of aligning the reflective unit with the LED pixel includes:

[0032] The first mark is formed on the reflector;

[0033] Align the first mark with the second mark located on the substrate to align the position of the reflective unit with that of the LED pixel.

[0034] In some embodiments, providing a first mark, the step of forming the first mark on the reflector includes:

[0035] A photoresist layer is formed on the mirror by photolithography;

[0036] The first mark is formed by dry etching.

[0037] In some embodiments, the thickness of the first mark is less than or equal to the thickness of the reflector. The first mark is for aligning the reflective unit with the driving circuit, and the depth of the first mark may extend into the surface of the LED epitaxial layer.

[0038] In some embodiments, the first mark is located at the edge of the reflector.

[0039] In some embodiments, the edge portion of the reflector specifically refers to the two sides corresponding to the flat edge of the wafer, and the first mark should be recognizable by the lithography machine.

[0040] In some embodiments, aligning the reflective unit with the driving circuit before bonding the substrate to the LED epitaxial layer includes:

[0041] A conductive layer is formed on the reflective unit;

[0042] An adhesion layer is formed on the substrate;

[0043] The conductive layer comes into contact with the adhesive layer to form a bonding layer.

[0044] In some embodiments, the reflective unit includes a first surface and a second surface, the first surface being in contact with the first doped semiconductor layer, and the second surface being in contact with the bonding layer. The reflective unit is covered by the bonding layer and the first doped semiconductor layer and corresponds to an LED pixel.

[0045] In some embodiments, the LED pixels are electrically connected to the corresponding contacts to form an electrical connection structure that enables the contacts to independently drive the corresponding LED pixels, including:

[0046] An electrode layer is formed on the LED pixel, and the electrode layer is electrically connected to the second doped semiconductor layer and the contact.

[0047] In some embodiments, before forming an electrode layer on the LED pixel, the following steps are included:

[0048] A passivation layer is formed on the LED pixel;

[0049] A first opening is formed in the passivation layer corresponding to the second doped semiconductor layer; the first opening exposes the second doped semiconductor layer;

[0050] A second opening is provided on the passivation layer corresponding to the contact point, the second opening exposing the contact point;

[0051] The electrode layer is electrically connected to the second doped semiconductor layer and the contact through the first opening and the second opening, respectively.

[0052] In some embodiments, a reflector is provided, and the step of forming the reflector on the LED epitaxial layer includes:

[0053] The reflector is formed on the epitaxial layer of the LED by vacuum evaporation or magnetron sputtering.

[0054] In some embodiments, the reflector is selected from any one or more combinations of Ag, Al, Ni, Ti, and W. The metal of the reflector has high reflectivity, preferably Ag.

[0055] In some embodiments, the thickness of the reflector is between 20 and 200 nm.

[0056] In some embodiments, providing LED pixels, prior to the step structure formed by etching the LED epitaxial layer, includes:

[0057] The LED epitaxial layer is thinned, and the thinning process includes etching or polishing.

[0058] In some embodiments, the bonding layer is selected from any one of metal, photoresist, polyimide, and polydimethylsiloxane. The material of the bonding layer must be such that it will not be corroded by the etchant used to remove the mask, thereby preventing the etchant from seeping into the reflective element.

[0059] In some embodiments, a miniature light-emitting diode display chip includes:

[0060] substrate;

[0061] LED pixels, wherein the LED pixel array is arranged on the substrate;

[0062] A bonding layer is located between the substrate and the LED pixel;

[0063] A reflective unit is provided, wherein the reflective unit array is arranged between the LED pixel and the bonding layer, the reflective unit is disposed corresponding to the LED pixel, and the bonding layer covers the reflective unit.

[0064] In some embodiments, the active layer can be a multi-quantum-well structure to confine electron and hole carriers to the quantum well region. When electrons and holes recombine, the carriers will emit photons after radiative recombination, converting electrical energy into light energy.

[0065] In some embodiments, the first doped semiconductor layer and the second doped semiconductor layer may include one or more layers based on IIVI materials such as ZnSe or ZnO or IIIV nitride materials such as GaN, AlN, InN, InGaN, GaP, AlInGaP, AlGaAs, and alloys thereof.

[0066] In some embodiments, the LED pixels are formed on an LED epitaxial layer, the LED epitaxial layer including a first doped semiconductor layer, a second doped semiconductor layer and an active layer located between the two; the first doped semiconductor layer is a continuous functional layer structure, and the second doped semiconductor layer has a plurality of mesa structures arranged in an array, thereby forming the LED pixels arranged in an array on the LED epitaxial layer.

[0067] In some embodiments, the second doped semiconductor layer can be ion implanted to form the LED pixels arranged in an array.

[0068] In some embodiments, the substrate includes a driving circuit and a plurality of contacts connected to the driving circuit. The contacts are located between adjacent LED pixels, and the LED pixels are electrically connected to the corresponding contacts so that the LED pixels can be driven independently by the corresponding contacts.

[0069] In some embodiments, the LED pixel has a passivation layer and an electrode layer; the passivation layer is located on the second doped semiconductor layer and has a first opening corresponding to the second doped semiconductor layer and a second opening corresponding to the contact; the electrode layer is located on the passivation layer and is electrically connected to the second doped semiconductor layer and the contact through the first opening and the second opening.

[0070] In some embodiments, the orthographic projection of the reflective unit on the substrate at least covers the orthographic projection of the active layer corresponding to the LED pixel on the substrate.

[0071] In some embodiments, the patterned reflective unit is shaped like a frustum, and its top view is circular.

[0072] In some embodiments, the reflective unit is obtained by patterning a mirror formed on the LED epitaxial layer. A first mark is formed on the mirror for alignment with a second mark located on the driving circuit. The size of the first mark is slightly larger than the bottom diameter of the stepped structure, but it cannot extend to the opening of the continuous first doped semiconductor layer to prevent the emitter metal from being etched during etching.

[0073] In some embodiments, the thickness of the first mark is less than or equal to the thickness of the reflector.

[0074] In some embodiments, the LED pixels are miniature light-emitting diodes, and the LED pixels are arranged in an array.

[0075] In some embodiments, when the second doped semiconductor layer of each LED pixel is electrically isolated from each other, the active layers of adjacent LED pixels are electrically isolated, and the first doped semiconductor layers of adjacent LED pixels are electrically connected.

[0076] In some embodiments, the substrate is a silicon-based CMOS driving substrate or a thin-film field-effect transistor driving substrate.

[0077] In some embodiments, the thickness of the stepped structure is greater than or equal to the thickness of the second doped semiconductor layer.

[0078] Beneficial Effects: Compared with the prior art, the fabrication method of the micro light-emitting diode display chip of the present invention includes: providing a substrate; providing an LED epitaxial layer, the LED epitaxial layer being disposed on the substrate; forming a reflector on the LED epitaxial layer; patterning the reflector to form a plurality of reflective units arranged in an array; forming a bonding layer on the substrate and / or the LED epitaxial layer, the bonding layer covering the reflective units, and bonding the substrate and the LED epitaxial layer; removing the substrate; forming a plurality of LED pixels arranged in an array on the LED epitaxial layer; the reflective units are located between the corresponding LED pixels and the bonding layer. By patterning the reflector, on the one hand, the problem of corrosion of reflective units caused by the penetration of etching solution during wet mask removal can be solved. Since the patterned reflective units and LEDs can be set one-to-one with the LED pixels, the probability of contact between the reflective units and the etching solution is reduced, avoiding bulging in this area and improving the conductivity and adhesion of the LED pixels. On the other hand, the influence of metal sputtering of the reflector on device leakage current is avoided in the pixel isolation process.

[0079] The present invention discloses a micro light-emitting diode (LED) display chip comprising: a substrate; LED pixels arranged in an array on the substrate; a bonding layer located between the substrate and the LED pixels; and a reflective unit array arranged between the LED pixels and the bonding layer, wherein the reflective units are correspondingly disposed to the LED pixels, and the bonding layer covers the reflective units. The present invention employs a vertical structure, and the introduction of a reflector enables the vertically structured micro LED display chip to emit light from one side, significantly improving external quantum efficiency and stability. Furthermore, the reflector is located only at the bottom of the LED pixels, reducing its length and decreasing the probability of the etchant contacting the reflective unit during wet mask removal. It also avoids etching the reflective unit during subsequent pixel isolation, preventing sputtering of materials such as metal from the reflective unit. Attached Figure Description

[0080] The technical solution and other beneficial effects of the present invention will become apparent from the following detailed description of specific embodiments of the invention, in conjunction with the accompanying drawings.

[0081] Figure 1 A top view of a micro light-emitting diode display chip structure according to some embodiments of this application is shown;

[0082] Figure 2 A cross-sectional view of a micro light-emitting diode display chip structure according to some embodiments of this application is shown;

[0083] Figure 3 A schematic diagram of the surface markings of a mirror according to some embodiments of this application is shown;

[0084] Figure 4 A schematic cross-sectional view of a substrate and a substrate according to some embodiments of this application is shown;

[0085] Figure 5 A schematic diagram of the bonding layer and reflector according to some embodiments of this application is shown;

[0086] Figure 6 A schematic diagram of a patterned mirror structure according to some embodiments of this application is shown;

[0087] Figure 7 A cross-sectional schematic diagram of the structure obtained after bonding an LED epitaxial layer to a substrate according to some embodiments of this application is shown;

[0088] Figure 8 A schematic cross-sectional view of the structure obtained after etching the step structure according to some embodiments of this application is shown;

[0089] Figure 9 A top view of the structure obtained after etching the step structure according to some embodiments of this application is shown;

[0090] Figure 10 A cross-sectional schematic diagram of the structure obtained after setting the second opening according to some embodiments of this application is shown;

[0091] Figure 11 A top view of the structure obtained after setting the second opening according to some embodiments of this application is shown;

[0092] Figure 12 A schematic cross-sectional view of the structure obtained after forming a passivation layer according to some embodiments of this application is shown;

[0093] Figure 13 A top view of the structure obtained after forming a passivation layer according to some embodiments of this application is shown;

[0094] Figure 14 A schematic diagram of a reflective unit structure according to some embodiments of this application is shown;

[0095] Reference numerals: 100-Miniature LED display chip, 101-Substrate, 102-Bonding layer, 103-First doped semiconductor layer, 104-Second doped semiconductor layer, 105-Active layer, 106-Passivation layer, 107-Electrode layer, 108-LED pixel, 109-Contact, 110-First opening, 111-Second opening, 112-Substrate, 113-Conductive layer, 114-Reflector, 115-LED epitaxial layer, 116-Conductive layer, 117-Adhesion layer, 118-First marker, 1141-Reflective unit, 1142-First surface, 1143-Second surface. Detailed Implementation

[0096] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0097] This invention discloses many different embodiments or examples for implementing different structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described herein. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0098] Generally, terms can be understood at least in part according to the usage of the present invention. For example, the term "one or more" as used herein, at least in part according to the present invention, can be used to describe any component, structure, or feature in the singular, or in the plural, to describe a combination of components, structures, or features. Similarly, terms such as "a," "an," or "the" can also be understood, at least in part according to the present invention, to convey either a singular or a plural usage. Furthermore, the term "based on..." can be understood not necessarily to convey an exclusive set of factors, but rather, at least in part according to the present invention, can alternatively allow for the presence of additional factors that do not necessarily have to be explicitly described.

[0099] It should be readily understood that the meanings of “on,” “above,” and “on top of” in this invention should be interpreted in the broadest sense, such that “on” means not only “directly on something,” but also “on something” including the presence of an intermediate component or layer between the two, and “on something” or “above something” means not only “on something” or “above something,” but also “on something” or “above something” where no intermediate component or layer between the two exists.

[0100] Furthermore, for ease of description, spatial relative terms such as "below," "under," "lower," "above," and "upper" may be used in this invention to describe the relationship of one element or component to another element or component shown in the accompanying drawings. In addition to the orientations described in the figures, the spatial relative terms are also intended to cover different orientations of the device during use or operation. The device may be oriented in other ways (rotated 90° or otherwise), and the spatial relative descriptive terms used in this invention can be interpreted accordingly.

[0101] As used in this invention, the term "layer" refers to a portion of material comprising a region of a certain thickness. A layer may extend over the entire lower or upper layer structure, or may have a extent smaller than that of the lower or upper layer structure. Furthermore, a layer may be a region of a homogeneous or heterogeneous continuous structure with a thickness less than the thickness of the continuous structure. For example, a layer may be located between the top and bottom surfaces of a continuous structure, or between any pair of horizontal planes therebetween. A layer may extend horizontally, vertically, and / or along a tapered surface. A substrate may be a single layer, which may include one or more layers, and / or may have one or more layers on, above, and / or below it. A single layer may include multiple layers. For example, a semiconductor layer may include one or more doped or undoped semiconductor layers, and may have the same or different materials.

[0102] In this invention, the positional relationship between "upper" and "lower" is respectively related to the appendix. Figure 2 The top and bottom correspond to each other, with appendix. Figure 2 The upper center is the light-emitting direction, and the upper surface of pixel 108 is the light-emitting surface.

[0103] As used in this invention, the term "substrate" refers to a material on which subsequent material layers are added. The substrate itself may be patterned. The material added on top of the substrate may be patterned or may remain unpatterned. Furthermore, the substrate may comprise a wide variety of semiconductor materials, such as silicon, silicon carbide, gallium nitride, germanium, gallium arsenide, indium phosphide, etc. Alternatively, the substrate may be made of a non-conductive material, such as glass, plastic, or sapphire wafer. Further alternatively, the substrate may have semiconductor devices or circuits formed therein.

[0104] As used in this invention, "micro" LED and "micro" device refer to the descriptive dimensions of certain devices or structures according to embodiments of this application. The term "micro" device or structure as used in this invention is intended to indicate a scale of 100 nanometers to 100 micrometers. However, it should be understood that embodiments of the invention are not necessarily limited thereto, and certain aspects of the embodiments can be applied to larger and possibly smaller size scales.

[0105] The display device of this invention uses a Micro-LED (Micro light-emitting diode) structure, with the size of the micro-LED reduced to 100 nanometers to 100 micrometers. In Micro-LEDs, the Micro-LED array is highly integrated, and the distance between the pixels of the Micro-LEDs in the array is further reduced to the 5-micrometer level. The Micro-LED display method involves connecting Micro-LED chips of 5-micrometer size or even smaller to a driving panel, achieving precise control over the light emission brightness of each Micro-LED chip. The manufacturing method of this invention is applicable to Micro-LED structures, enabling the fabrication of miniature display devices.

[0106] In some embodiments, the term substrate 101 as used in this invention refers to the material on which subsequent material layers are added. The substrate 101 itself may be patterned. The material added to the top of the substrate 101 may be patterned or may remain unpatterned. The substrate 101 may be, for example, but not limited to, a display substrate including a CMOS (Complementary Metal Oxide Semiconductor) backplane or a TFT glass substrate. Then, an LED epitaxial layer 115 forms pixel points 108 on the substrate 101. In some embodiments, the functional epitaxial layer is partially patterned / etched, allowing thin, continuous functional layers and bonding layers to be retained to avoid potential functional pixel peeling. Additionally, the manufacturing method in this application can further reduce physical damage to the sidewalls of functional pixels, reduce damage to the quantum well structure of the light-emitting region of the pixel, and improve the optical and dot-blood properties of the functional pixels.

[0107] In some embodiments, the LED pixel 108 in this invention is selected from micro light-emitting diodes, and the structure of the LED pixel 108 can be common cathode, common anode, or each independent.

[0108] In some embodiments, the common cathode structure is achieved by connecting a continuous series of cathode electrodes. In some embodiments, a common anode structure or independent structures can also be used, as long as the LED pixels 108 can emit light normally.

[0109] Figure 1 A top view of the structure of a miniature light-emitting diode display chip 100 according to some embodiments is shown. Figure 2 It shows Figure 1 A cross-sectional view of the structure of a micro LED display chip 100 along line A-A'. The micro LED display chip 100 structure includes a substrate 101 and at least two LED pixels 108. The LED pixels 108 are disposed on the substrate 101; it also includes a reflective unit 1141 disposed between the bonding layer 102 and the LED pixels 108, the reflective unit 1141 being obtained through patterning; it also includes a passivation layer 106 formed on the pixels 108; and it includes an electrode layer 107 formed on the passivation layer 106, electrically connected to the LED pixels 108 and the substrate 101 respectively.

[0110] In some embodiments, substrate 101 may include semiconductor materials such as silicon, silicon carbide, germanium nitride, germanium arsenide, and indium phosphide. In some embodiments, substrate 101 may have driving circuitry formed therein, and substrate 101 may be a CMOS backplane or a TFT glass substrate. The driving circuitry provides electrical signals to pixel 108 to control brightness. In some embodiments, the driving circuitry may include an active matrix driving circuit, wherein each individual pixel 108 corresponds to an independent driver. In some embodiments, substrate 101 is provided with contacts 109 connected to the driving circuitry, the contacts 109 being exposed between two adjacent reflectors 114, each pixel 108 being independently driven by a different driving circuitry, and each pixel 108 being able to operate independently. In some embodiments, the driving circuitry is an IC driving circuit.

[0111] See Figure 2 Pixel 108 includes a mesa structure formed by etching the LED epitaxial layer 115. The mesa structure includes a first doped semiconductor layer 103 and a second doped semiconductor layer 104. A bonding layer 102 is formed on the substrate 101, the first doped semiconductor layer 103 is formed on the bonding layer 102, and the second doped semiconductor layer 104 is formed on the first doped semiconductor layer 103. In some embodiments, the first doped semiconductor layer 103 is a continuous functional layer structure, and the second doped semiconductor layer 104 is patterned, or the second doped semiconductor layer 104 is etched to form a mesa structure, or the second doped semiconductor layer 104 is ion implanted to form the LED pixel 108. In some embodiments, an active layer 105 is formed between the first doped semiconductor layer 103 and the second doped semiconductor layer 104 of each LED pixel 108. In some embodiments, the active layer 105 is a multiple quantum well (MQW) layer, where electrons and holes recombine in the quantum well region to generate photons, thereby achieving light emission.

[0112] See Figure 2 MESA etching forms a mesa structure on the LED epitaxial layer 115, with the thickness of the mesa structure being greater than the thickness of the second doped semiconductor layer 104. In some embodiments, the thickness of the mesa structure can also be equal to the thickness of the second doped semiconductor layer 104, meaning the top surface of the first doped semiconductor layer 103 is not exposed during etching. In some embodiments, the cross-section of the mesa structure is trapezoidal, and the tilt angle of the trapezoid can be defined by the etching process, so that each LED pixel 108 is a trapezoidal structure and forms a trapezoidal pixel array. The trapezoidal sidewalls help improve the luminous efficiency of the pixels, mainly because the trapezoidal sidewalls can reflect light and reflect it back to the light extraction sidewalls. In some embodiments, the cross-section of the mesa structure can be rectangular, so that the LED pixel 108 has a structure with vertical sides.

[0113] In some embodiments, the first doped semiconductor layer 103 is a continuous functional layer structure. The first doped semiconductor layer 103 extends across multiple LED pixels 108 and forms the common anode of these LED pixels 108. The second doped semiconductor layer 104 is partially patterned or etched to form a mesa structure. The second doped semiconductor layers 104 of different LED pixels 108 are electrically isolated from each other, so each LED pixel 108 can have a cathode with a different voltage level than other units. In some embodiments, the first doped semiconductor layer 103 extending across the LED pixels 108 can be relatively thin. By having a continuous first doped semiconductor layer 103 on each LED pixel 108, the bonding area between the substrate 101 and the multiple LED pixels 108 is not limited to the area below the second doped semiconductor layer 104, but also extends to the area between each LED pixel 108. Therefore, by providing a continuous first doped semiconductor layer 103, the area of ​​the bonding layer 102 is increased. Therefore, the bonding strength between the substrate 101 and the multiple LED pixels 108 is enhanced, and the risk of structural peeling of the micro LED display chip 100 can be reduced.

[0114] In some embodiments, the first doped semiconductor layer 103 and the second doped semiconductor layer 104 may comprise one or more layers based on IIVI materials (such as ZnSe or ZnO) or IIIV nitride materials (such as GaN, AlN, InN, InGaN, GaP, AlInGaP, AlGaAs, and alloys thereof). In some embodiments, the first doped semiconductor layer 103 is p-type gallium nitride, and the second doped semiconductor layer 104 is n-type gallium nitride.

[0115] The bonding layer 102 is an adhesive material layer formed on the substrate 101 or the LED epitaxial layer 115 to bond the substrate 101 and the LED pixel 108. In some embodiments, the bonding layer 102 may include a conductive material, such as a metal or metal alloy. In some embodiments, the bonding layer 102 may include Au, Sn, In, Cu, or Ti. In some embodiments, the bonding layer 102 may include a non-conductive material, such as polyimide (PI) or polydimethylsiloxane (PDMS). In some embodiments, the bonding layer 102 may include a photoresist, such as SU-8 photoresist.

[0116] See Figure 2 A passivation layer 106 is disposed on a portion of the second doped semiconductor layer 104 and the first doped semiconductor layer 103. The passivation layer 106 is used to protect and isolate the LED pixel 108. In some embodiments, the passivation layer 106 may include SiO2, Al2O3, SiN or other suitable materials. In some embodiments, the passivation layer 106 comprises polyimide, SU-8 photoresist or other photo-patternable polymers.

[0117] See Figure 2 A first opening 110 is formed on the passivation layer 106 exposing the second doped semiconductor layer 104, and a second opening 111 is formed on the passivation layer 106 exposing the contact 109. An electrode layer 107 is formed on the first opening 110 and the second opening 111, and the electrode layer 107 is electrically connected to the second doped semiconductor layer 104 and the contact 109. In some embodiments, the first opening 110 is located at the center of each LED pixel 108, and the second opening 111 is located at the gap between adjacent pixels 108. In some embodiments, the electrode layer 107 may be a conductive material, such as indium tin oxide (ITO), Cr, Ti, Pt, Au, Al, Cu, Ge, or Ni.

[0118] In some embodiments, the micro LED display chip 100 adopts a vertical structure. Compared with the horizontal structure, the vertical structure, with its P and N electrodes arranged on opposite sides, vertical current conduction, and substrate conductivity, can perfectly solve the problems of poor thermal conductivity, current congestion effect, and electrode light absorption effect present in the horizontal structure, and thus can withstand high current overdrive. For the micro LED display chip 100, the key to improving brightness lies in the ohmic contact of the first doped semiconductor layer 103. This is because the first doped semiconductor layer 103 needs to serve as both an ohmic contact electrode and an optical reflector, therefore, a reflective unit 1141 needs to be provided on the first doped semiconductor layer 103.

[0119] See Figure 14A reflective unit 1141 is located between the LED pixel 108 and the bonding layer 102 to improve light reflection. The reflective unit 1141 includes a first surface 1142 and a second surface 1143. The first surface 1142 contacts the first doped semiconductor layer 103, and the second surface 1143 contacts the bonding layer 102. In some embodiments, the reflective unit 1141 is completely covered by the bonding layer 102 and is configured one-to-one with each LED pixel 108. In some embodiments, the reflective unit 1141 can be any one or more combinations of Ag, Al, Ni, Ti, and W, wherein Ag has the highest emissivity in the visible light band. In some embodiments, to improve the adhesion of Ag, multi-metal composite electrodes such as Ti / Ag or Ag / Al / Ni can be used to simultaneously obtain ground contact resistance and high reflectivity. In some embodiments, to improve the adhesion of the Ag mirror, a conductive metal film and Ni metal can be added between the Ag mirror and the first doped semiconductor layer 103, which improves the adhesion between the conductive film and the NiAg layer while protecting the first doped semiconductor layer 103. In some embodiments, the thickness of the reflective unit 1141 needs to be controlled between 20 and 200 nm. In some embodiments, when a multi-metal composite electrode is used, the thickness of the Ag layer is 20 to 100 nm, and the thickness of the Ni layer is 5 to 20 nm. In some embodiments, the reflective units 1141 are spaced apart, and the orthographic projection of the reflective unit 1141 on the substrate 101 at least covers the orthographic projection of the active layer 105 of the corresponding LED pixel 108 on the substrate 101. This ensures that light emitted from at least the active layer 105 can be reflected by the reflective unit 1141. The reflective unit 1141 needs to meet certain size requirements, which must ensure both the reflection of light from the light-emitting area of ​​the LED pixel and the spacing between the reflective units 1141. In some embodiments, the patterning process is photolithography.

[0120] See Figure 3 A first mark 118 is formed on the reflector 114. The first mark 118 can be formed by photolithography and etching processes. The shape of the first mark 118 is a square or rectangular icon. The first mark 118 is used for subsequent alignment of the patterned reflector 114 with the IC driving circuit of the substrate 101. In some embodiments, the thickness of the first mark 118 is less than or equal to the thickness of the reflector 114, and the depth of the first mark 118 can extend into the surface of the LED epitaxial layer 115.

[0121] In some embodiments, the first mark 118 corresponds to the second mark located on the IC driving circuit of the substrate 101. In some embodiments, other bonding methods can also be used, as long as the position of the reflective unit 1141 and the driving circuit is aligned.

[0122] Figures 4 to 13 Cross-sectional views of different stages in the fabrication process of the micro LED display chip 100 are shown.

[0123] See Figure 4 A substrate 101 is provided, in which a driving circuit is formed and connected to a contact 109; a substrate 112 is provided, on which an LED epitaxial layer 115 is formed, and the LED epitaxial layer 115 includes a first doped semiconductor layer 103, a second doped semiconductor layer 104 and an active layer 105.

[0124] In some embodiments, substrate 101 is a silicon-based CMOS backplane or a thin-film field-effect transistor. Silicon-based CMOS is a chip made of silicon. In some embodiments, substrate 112 is a semiconductor material, such as silicon or gallium nitride, or substrate 112 is a non-conductive material, such as sapphire or glass. In some embodiments, the first doped semiconductor layer 103 is p-type gallium nitride, and the second doped semiconductor layer 104 is n-type gallium nitride.

[0125] In some embodiments, the LED epitaxial layer 115 is formed on the substrate 112 using MOCVD technology to complete the entire epitaxial process. MOCVD technology is a low-pressure sealed chamber in which a mixed carrier gas of N2 and H2 is used to transport the organic source to the reaction chamber. The substrate on the graphite disk is heated by radio frequency, so that the organic source undergoes a series of chemical reactions on the substrate surface, thereby performing the corresponding epitaxial growth.

[0126] See Figure 5 An adhesion layer 117 is formed on the substrate 101, a reflector 114 is formed on the LED epitaxial layer 115 of the substrate 112, and a mark is formed on the reflector 114. The position of the mark needs to correspond to the IC driving circuit of the driving circuit.

[0127] In some embodiments, the adhesion layer 117 may include a conductive material, such as a metal or metal alloy. In some embodiments, the adhesion layer 117 may include Au, Sn, In, Cu, or Ti. In some embodiments, the adhesion layer 117 may include a non-conductive material, such as polyimide (PI) or polydimethylsiloxane (PDMS). In some embodiments, the adhesion layer 117 may include a photoresist, such as SU-8 photoresist. In some embodiments, the reflector 114 is formed by electron beam evaporation or sputtering. In some embodiments, the reflector 114 is formed by any one or more combinations of Ag, Al, Ni, Ti, and W. In some embodiments, the process of forming the first mark 118 includes etching or evaporation. In some embodiments, a photoresist layer is formed on the reflector by photolithography; the photoresist layer is removed by dry etching to form the first mark 118. In some embodiments, the first mark 118 is square or rectangular in shape, the thickness of the first mark 118 is less than or equal to the thickness of the reflector 114, and the depth of the first mark 118 may extend into the surface of the LED epitaxial layer 115.

[0128] See Figure 6 The reflector 114 is patterned according to the position of the first mark 118 to obtain the reflector unit 1141. The reflector unit 1141 is a high reflectivity layer structure. Then, a conductive layer 116 is deposited on the reflector unit 1141.

[0129] In some embodiments, the patterning process employs photolithography, specifically including: first, forming a patterned photoresist layer on the mirror 114 using photolithography; then, patterning the mirror 114 using dry etching; and finally, removing the photoresist layer to obtain the patterned reflective unit 1141. In some embodiments, the deposition method includes evaporation or sputtering. In some embodiments, the conductive layer 116 is made of Au, Sn, In, Cu, or Ti. In some embodiments,

[0130] See Figure 7 The LED epitaxial layer 115 of the substrate 112 is flipped and bonded to the substrate 101 through the conductive layer 116 and the adhesive layer 117. The conductive layer 116 and the adhesive layer 117 are then formed into a single layer, namely the bonding layer 102. The bonding layer 102 completely covers the reflective unit 1141. Finally, the substrate 112 is removed from the LED epitaxial layer 115.

[0131] In some embodiments, the reflective unit 1141 is aligned and bonded to the driving circuit according to the position of the second comparison on the IC driving circuit and the first mark 118 of the reflector 114. In some embodiments, the bonding layer 102 may include one or more layer structures. After bonding is completed, the bonding layer 102 and the reflective unit 1141 may be collectively referred to as one layer, and the reflective unit 1141 is completely covered in the bonding layer 102. In some embodiments, the substrate 112 removal method includes, but is not limited to, laser lift-off, dry etching, wet etching, mechanical polishing, etc.

[0132] The flipped LED epitaxial layer 115 is thinned by means of dry etching, wet etching or mechanical polishing.

[0133] See Figure 8 and Figure 9 Following the MESA pattern designed using a patterned mask, an etching operation is performed to remove a portion of the second doped semiconductor layer 104 to expose the first doped semiconductor layer 103, forming a functionalized stepped structure. This stepped structure can serve as LED pixels 108; the LED pixels 108 are arranged in an array (e.g., Figure 9 (4×4 array in the image).

[0134] In some embodiments, an array of masks, such as photoresist, is formed on the second doped semiconductor layer 104 by photolithography. The mask is then etched onto the areas of the second doped semiconductor layer 104 not covered by the mask, exposing the active layer 105. Finally, the mask is removed using an etchant to form a mesa structure. Because the reflective unit 1141 is patterned, and due to the specific material limitations of the bonding layer 102, the possibility of etchant penetrating to the surface of the reflective unit 1141 is significantly reduced, minimizing damage to the reflective unit 1141.

[0135] In some embodiments, the etching depth of the etching operation is based on a predefined thickness achievable by the first doped semiconductor layer 103, which remains on the substrate 101. The retained first doped semiconductor layer 103 is continuous in the horizontal direction. After fabrication, the second doped semiconductor layer 104 in each pixel 108 can be electrically isolated, and the first doped semiconductor layers 103 between adjacent LED pixels 108 can be electrically connected. In some embodiments, the mesa structure is greater than or equal to the thickness of the second doped semiconductor layer. In some embodiments, the etching operation includes dry etching or wet etching.

[0136] See Figure 10 and Figure 11An etching operation can be performed to remove a portion of the first doped semiconductor layer 103 between the LED pixels 108, exposing the contacts 109. Since the reflective units 1141 are positioned corresponding to the LED pixels 108, there are no reflective units 1141 on the contacts 109, meaning that exposing the contacts 109 will not affect the reflective units. In some embodiments, the etching operation includes dry etching or wet etching.

[0137] See Figure 12 and Figure 13 A passivation layer 106 is formed on the LED pixel 108 to protect the LED pixel 108. In some embodiments, the passivation layer 106 is formed by chemical vapor deposition. In some embodiments, a second opening 111 is formed on the passivation layer 106, exposing a contact 109. In some embodiments, a first opening 110 is formed on the passivation layer 106, exposing a second doped semiconductor layer 104. In some embodiments, the first opening 110 and the second opening 111 can be formed by a photolithography process, using a photosensitive material (such as polyimide, SU-8 photoresist, or other photo-patternable polymers) to form the passivation layer 106.

[0138] See Figure 2 An electrode layer 107 is formed on the first opening 110, the second opening 111, the exposed second doped semiconductor layer 104, and a portion of the exposed first doped semiconductor layer 103. The electrode layer 107 connects the second doped semiconductor layer 104 to a contact 109. The driving circuit can control the voltage and current of the second doped semiconductor layer 104 through the contact 109. The contact 109 is located between adjacent LED pixels 108, and the electrical connection between the LED pixels 108 and the contact 109 allows each LED pixel 108 to be driven individually.

[0139] In some embodiments, by patterning the reflector 114, the light extraction efficiency of the micro LED display chip is improved while the impact of the reflector 114 on the device during subsequent etching is resolved. The patterned reflective unit 1141 is located only at the bottom of the corresponding LED pixel 108. On the one hand, this can significantly reduce the probability of corrosion of the reflector 114 by the etchant during wet mask removal. On the other hand, it also avoids the impact of sputtering of the reflector 114 on device leakage during the pixel isolation process.

[0140] The present invention has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the technical solutions and core ideas of the present invention. Those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for fabricating a miniature light-emitting diode display chip, characterized in that, include: A substrate (101) is provided, the substrate (101) having a second mark; An LED epitaxial layer (115) is provided, the LED epitaxial layer (115) being disposed on a substrate (112); A reflector (114) is formed on the LED epitaxial layer (115), and a first mark (118) is formed on the reflector (114). The thickness of the first mark (118) is less than or equal to the thickness of the reflector (114), and the depth of the first mark (118) extends into the surface of the LED epitaxial layer (115). The reflector (114) is patterned according to the position of the first mark (118) to form a plurality of reflective units (1141) arranged in an array; A bonding layer (102) is formed on the substrate (101) and / or the LED epitaxial layer (115), the bonding layer (102) covering the reflective unit (1141), and the substrate (101) and the LED epitaxial layer (115) are aligned and bonded according to the position of the first mark (118) and the position of the second mark; Remove the substrate (112); A plurality of LED pixels (108) are arranged in an array on the LED epitaxial layer (115); the reflective unit (1141) is located between the corresponding LED pixel (108) and the bonding layer (102), and the orthographic projection of the reflective unit (1141) on the substrate (101) at least covers the orthographic projection of the active layer (105) of the corresponding LED pixel (108) on the substrate (101).

2. The method for fabricating a micro light-emitting diode display chip according to claim 1, characterized in that, The LED epitaxial layer (115) includes a first doped semiconductor layer (103), a second doped semiconductor layer (104), and an active layer (105) located between the two; The first doped semiconductor layer (103) is a continuous functional layer structure. The second doped semiconductor layer (104) is etched to form a mesa structure, forming the LED pixel points (108) arranged in an array.

3. The method for fabricating a micro light-emitting diode display chip according to claim 2, characterized in that, The step of etching the second doped semiconductor layer (104) to form a mesa structure includes: A patterned mask is formed on the second doped semiconductor layer (104); The area on the second doped semiconductor layer (104) not covered by the mask is etched, and the etching depth is at least the depth of the second doped semiconductor layer (104); Remove the mask to form the mezzanine structure.

4. The method for fabricating a micro light-emitting diode display chip according to claim 2, characterized in that, The substrate (101) includes a driving circuit and a plurality of contacts (109) connected to the driving circuit. The contacts (109) are located between adjacent LED pixels (108). The LED pixels (108) are electrically connected to the corresponding contacts (109) so that the LED pixels (108) can be driven independently by the corresponding contacts (109).

5. The method for fabricating a micro light-emitting diode display chip according to claim 1, characterized in that, The steps of patterning the reflector (114) to form an array of multiple reflective units (1141) and bonding the substrate (101) to the LED epitaxial layer (115) include: A photoresist layer is formed on the reflector (114) by photolithography; The reflector (114) is patterned by dry etching, and then the photoresist layer is removed to form the reflective unit (1141); Align the position of the reflective unit (1141) with the driving circuit of the substrate (101) so that the substrate (101) is bonded to the LED epitaxial layer (115).

6. The method for fabricating a micro light-emitting diode display chip according to claim 4, characterized in that, The LED pixel (108) is electrically connected to the corresponding contact (109), including: An electrode layer (107) is formed on the LED pixel (108), and the electrode layer (107) is electrically connected to the second doped semiconductor layer (104) and the contact (109).

7. The method for fabricating a micro light-emitting diode display chip according to claim 6, characterized in that, Before forming the electrode layer (107) on the LED pixel (108), the following is included: A passivation layer (106) is formed on the LED pixel (108); A first opening (110) is provided on the passivation layer (106) corresponding to the second doped semiconductor layer (104), penetrating the passivation layer (106), and the first opening (110) exposes the second doped semiconductor layer (104); A second opening (111) is provided on the passivation layer (106) corresponding to the contact (109), penetrating the passivation layer (106), and the second opening (111) exposes the contact (109); The electrode layer (107) is electrically connected to the second doped semiconductor layer (104) and the contact (109) through the first opening (110) and the second opening (111), respectively.

8. The method for fabricating a micro light-emitting diode display chip according to claim 1, characterized in that, The reflector (114) is selected from any one or more combinations of Ag, Al, Ni, Ti, and W; the bonding layer is selected from any one of metal, photoresist, polyimide, and polydimethylsiloxane.

9. A miniature light-emitting diode display chip, characterized in that, include: A substrate (101) having a second mark; LED pixels (108), the LED pixels (108) array is arranged on the substrate (101); A bonding layer (102) is located between the substrate (101) and the LED pixel (108); A reflector (114) is provided with a first mark (118) and includes a plurality of reflective units (1141). The positions of the first mark (118) and the second mark are aligned. The thickness of the first mark (118) is less than or equal to the thickness of the reflector (114), and the depth of the first mark (118) extends into the surface of the epitaxial layer (115) where the LED pixel (108) is located. The array of reflective units (1141) is arranged between the LED pixel (108) and the bonding layer (102). The reflective units (1141) are correspondingly arranged with the LED pixel (108). The bonding layer (102) covers the reflective units (1141), and the orthographic projection of the reflective units (1141) on the substrate (101) at least covers the orthographic projection of the active layer (105) corresponding to the LED pixel (108) on the substrate (101).

10. The miniature light-emitting diode display chip according to claim 9, characterized in that, The LED pixel (108) is formed on the LED epitaxial layer (115), which includes a first doped semiconductor layer (103), a second doped semiconductor layer (104), and an active layer (105) located between the two. The first doped semiconductor layer (103) is a continuous functional layer structure, and the second doped semiconductor layer (104) has multiple mesa structures arranged in an array, thereby forming the LED pixel (108) arranged in an array on the LED epitaxial layer (115).

11. The miniature light-emitting diode display chip according to claim 10, characterized in that, The substrate (101) includes a driving circuit and a plurality of contacts (109) connected to the driving circuit. The contacts (109) are located between adjacent LED pixels (108). The LED pixels (108) are electrically connected to the corresponding contacts (109) so that the LED pixels (108) can be driven independently by the corresponding contacts (109).

12. The miniature light-emitting diode display chip according to claim 11, characterized in that, The LED pixel (108) has a passivation layer (106) and an electrode layer (107); The passivation layer (106) is located on the second doped semiconductor layer (104) and has a first opening (110) corresponding to the second doped semiconductor layer (104) and a second opening (111) corresponding to the contact (109); The electrode layer (107) is located on the passivation layer (106) and is electrically connected to the second doped semiconductor layer (104) and the contact (109) through the first opening (110) and the second opening (111).

13. The miniature light-emitting diode display chip according to claim 9, characterized in that, The reflective unit (1141) is obtained by patterning a reflector (114) formed on the LED epitaxial layer (115).

14. The miniature light-emitting diode display chip according to claim 9, characterized in that, The substrate (101) is a silicon-based CMOS driving substrate or a thin-film field-effect transistor driving substrate.

15. The miniature light-emitting diode display chip according to claim 9, characterized in that, The reflective unit (1141) is selected from any one or more combinations of Ag, Al, Ni, Ti, and W; the bonding layer (102) is made of any one of metal, photoresist, polyimide, and polydimethylsiloxane.

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