Semiconductor structures for microleds

Abstract

The proposed solution relates to a semiconductor structure (80) for a micro light emitting diode (micro LED) comprising an epitaxial wafer (10) and a plurality of InGaN lamellas (100) monolithically grown on the epitaxial wafer. Each InGaN wafer includes a QW layer. The plurality of InGaN flakes include individual InGaN flakes configured for red, green, and blue light emissions, respectively. The QW layers are disposed at different heights (hB, hG, hR) above the epitaxial wafer surface in a respective InGaN wafer (100), where the heights are related to emission wavelengths. The solution further relates to a micro LED device (800) comprising the semiconductor structure, and a method of manufacturing the semiconductor structure.

Description

(19) State Intellectual Property Office (12) Invention Patent Application (10) Application Publication Number (43) Application Publication Date (21) Application Number 202480058497.4 (22) Application Date 2024.06.25 (30) Priority Data 23197586.3 2023.09.15 EP (85) PCT International Application Entering National Phase Date 2026.03.12 (86) PCT International Application Application Data PCT / EP2024 / 067853 2024.06.25 (87) PCT International Application Publication Data WO2025 / 056207 EN 2025.03.20 (71) Applicant: Hexagonal Drill Company Address: Lund, Sweden (72) Inventors: L. Samuelsen, Björk, M. Herling, M. Berg (74) Patent Agency: China Patent Agency (Hong Kong) Limited 72001 Patent Attorneys: Zhang Qilu, Lin Yibin (51) Int.Cl. H10H 29 / 30 (2025.01) H10H 29 / 01 (2025.01) H10H 20 / 812 (2025.01) H10H 20 / 01 (2025.01) (54) Invention Title: Semiconductor Structure for MicroLEDs (57) Abstract: The proposed solution relates to a semiconductor structure (80) for micro light-emitting diodes (microLEDs), comprising an epitaxial wafer (10) and multiple InGaN wafers (100) monolithically grown on the epitaxial wafer. Each InGaN wafer contains a QW layer. The plurality of InGaN wafers include individual InGaN wafers respectively configured for red, green, and blue light emission. The QW layer is disposed at different heights (hB, hG, hR) above the epitaxial wafer surface in the respective InGaN wafer (100), wherein the height is related to the emission wavelength. The solution further relates to a microLED device (800) comprising the semiconductor structure, and a method for manufacturing the semiconductor structure.Claims 2 pages, Description 14 pages, Drawings 11 pages, CN 121866871 A 2026.04.14 CN 1 21 86 68 71 A 1. A semiconductor structure (80) for a micro light-emitting diode (microLED), comprising: an epitaxial wafer (10); a plurality of InGaN wafers (100B, 100G, 100R) monolithically grown on the epitaxial wafer, each comprising a quantum well (QW) layer (111, 112, 113); wherein the plurality of InGaN wafers comprises individual InGaN wafers respectively configured for emitting red, green and blue light, characterized in that the QW layers are disposed at different heights (hB, hG, hR) above the surface of the epitaxial wafer in the respective InGaN wafers (100), wherein the height is related to the emission wavelength. 2. The semiconductor structure of claim 1, wherein the QW layer is disposed at an increasing height in InGaN wafers configured for different emission wavelengths in a blue-green-red sequence. 3. The semiconductor structure of claim 1 or 2, wherein each InGaN wafer comprises a substrate layer (61) with a first indium concentration adjacent to the epitaxial wafer, and a buffer layer (62B, 62G, 62R) with a second indium concentration between the substrate layer and the QW layer, wherein the second indium concentration differs between InGaN wafers configured for different color emission. 4. The semiconductor structure of claim 3, wherein the substrate layer in each InGaN wafer has the same first indium concentration. 5. The semiconductor structure of claim 4, wherein the first indium concentration is 8-12%. 6. The semiconductor structure of any one of claims 3-5, wherein in InGaN wafers configured for blue emission, the second indium concentration is lower than the first indium concentration. 7. The semiconductor structure of any one of claims 3-6, wherein in InGaN wafers configured for blue emission, the second indium concentration is 5-10%. 8. The semiconductor structure according to any one of claims 3-7, wherein in the InGaN wafers respectively configured for green and red emission, the second indium concentration is higher than the first indium concentration. 9. The semiconductor structure according to any one of claims 3-8, wherein in the InGaN wafer configured for green emission, the second indium concentration is 10-15%. 10. The semiconductor structure according to any one of claims 3-9, wherein in the InGaN wafer configured for red emission, the second indium concentration is 18-20%. 11. The semiconductor structure according to any one of the preceding claims, wherein the InGaN wafer (100) has a truncated pyramidal shape having a top c-face surface connectable to a driving circuit to generate light emission.12. The semiconductor structure according to any one of the preceding claims, wherein the InGaN wafers (100) configured for the same emission wavelength are arranged in a hexagonal pattern on the epitaxial wafer. 13. The semiconductor structure according to any one of the preceding claims, wherein the InGaN wafers are arranged in groups of adjacent InGaN wafers on the epitaxial wafer. 14. The semiconductor structure according to claim 13, wherein each group comprises a ternary group of adjacent InGaN wafers (100) arranged in a triangular pattern. 15. The semiconductor structure according to claim 13 or 14, wherein each group comprises InGaN wafers (100) configured for blue, green, and red emission. 16. The semiconductor structure according to any one of claims 1-14, wherein the InGaN wafers (100) are arranged in groups, the groups being configured for the same emission wavelength, and wherein the spacing (PP) between the InGaN wafers within a respective group is related to the emission wavelength for which the InGaN wafers are configured, such that the spacing increases in the order of blue-green-red. Claims 1 / 2 Page 2 CN 121866871 A 17. A micro LED device (800) comprising: a semiconductor structure (80) according to any one of the preceding claims; and a driving circuit (84) connected via p-contacts (82B, 82G, 82R) to a respective top position of each InGaN wafer and via n-contacts (83) to the substrate side of an epitaxial wafer, for generating light emission from the respective InGaN wafer. 18. A method of manufacturing a semiconductor structure for a microLED, the method comprising: epitaxially growing an InGaN pyramid (5) through a mask window of an epitaxial wafer (10); truncating the InGaN pyramid to form truncated InGaN pyramids (40B, 40G, 40R) having a c-face top surface; growing quantum well (QW) layers (111, 112, 113) on the respective truncated InGaN pyramids; and growing a top InGaN layer on the respective QW layer to form separate InGaN wafers (100B, 100G, 100R) respectively configured for red, green, and blue light emission, characterized in that the QW layers are grown at different heights (hB, hG, hR) above the surface of the epitaxial wafer in the respective InGaN wafers (100), wherein the height is related to the emission wavelength. 19. The method of claim 18, wherein the QW layer is grown at increasing height in an InGaN wafer configured for different emission wavelengths in a blue-green-red order.20. The method of claim 18 or 19, wherein the truncated InGaN pyramid forms a corresponding substrate layer having a first indium concentration, the method further comprising: growing a buffer layer (62B, 62G, 62R) having a second indium concentration on the substrate layer prior to growing the QW layer, wherein the second indium concentration is different between InGaN wafers configured for different color emission. 21. The method of claim 20, wherein the substrate layer in each InGaN wafer has the same first indium concentration. 22. The method of any one of claims 18 to 21, wherein the growth of quantum well layers on InGaN wafers for different emission wavelengths is performed in a common epitaxial process. Claims 2 / 2 Page 3 CN 121866871 A Semiconductor Structure Technology Field for MicroLEDs

[0001] This technology relates to the field of semiconductor structures, particularly to microLEDs (micro-light-emitting diodes) used in display and lighting applications. This field focuses on improving the efficiency, performance, and manufacturing process of microLEDs, which are known for their high brightness, low power consumption, long lifetime, and very fast response time and high modulation speed.

[0002] Background: MicroLEDs have emerged as a promising technology for high-resolution displays in various applications such as augmented reality (AR), virtual reality (VR), mixed reality (MR), smartwatches, and head-up displays (HUDs). These applications require small pixel sizes (typically less than 10 μm) to achieve high resolution and a compact form factor. Using microLEDs offers several advantages over competing technologies such as liquid crystal displays (LCDs) and organic light-emitting diodes (OLEDs), including higher brightness, longer lifetime, and lower power consumption.

[0003] However, at small pixel sizes, several challenges related to the fabrication and performance of microLEDs exist. One significant issue is the sharp loss of external quantum efficiency as pixel size decreases. This efficiency loss is primarily due to the increased impact of sidewall damage caused by dry etching. Therefore, developing efficient microLEDs with pixel sizes below 10 μm remains a challenge. Another issue is red-emitting microLEDs, where nitride microLEDs and AlInGaP microLEDs are unsatisfactory in terms of both efficiency and brightness.

[0004] Another challenge in the fabrication of microLEDs is the assembly of red, green, and blue (RGB) pixels for high-resolution displays. Currently, these three colors are fabricated on separate wafers using epitaxial methods, and those wafers need to be picked out and placed on the backplane / driving circuitry of the display to build an array of RGB pixels. Various technologies exist to achieve this, many of which are not yet technically mature.To date, no pick-and-place method has been successfully used to fabricate and assemble displays with pixel sizes below 10 μm.

[0005] For small displays, such as AR / VR / MR, smartwatches, etc., one possibility is to directly bond the LED wafer to the Si CMOS active driver circuit. This still requires assembling all three colors into RGB pixels. For pixel sizes above 10 μm, this can be achieved through several methods, including pick-and-place methods, mechanical stacking of all three color sources superimposed on each other, or multi-junction epitaxial layers connected during epitaxy, for example, via tunnel junctions. However, these methods are not suitable for pixel sizes below 10 μm.

[0006] Several methods have been proposed to address these challenges, such as directly growing red, green, and blue LEDs on the same epitaxial wafer (i.e., a semiconductor wafer with a common growth layer), making it possible to avoid the mass transfer of pick-and-place, and instead, attaching the LED to the CMOS chip using a single-step wafer bonding process. However, a technique is still lacking to achieve RGB epitaxial wafers with pixel sizes below 10 μm and as small as 1 μm for all three colors with external quantum efficiencies in the double-digit range.

[0007] In Bi, Gustafsson and Samuelson's "Bottom-up approaches to microLEDs emitting red, green and blue light based on GaN nanowires and relaxed InGaN platelets", December 8, 2022, Chin. Phys. B, 2023, Vol. 32(1): 018103, Special Issue: Special Topic - Physics in MicroLEDs and Quantum Dot Devices, Special Review - Physics in MicroLEDs and Quantum Dot Devices, the authors discuss the miniaturization of LEDs. This paper provides a review of efforts to realize microLEDs by direct bottom-up growth based on selective region metal-organic vapor phase epitaxy. In our approach, a single LED based on GaN nanowires or InGaN platelets is small to 1 μm. These nanoLEDs can serve as building blocks in arrays for assembling microLEDs of different sizes, avoiding sidewall damage caused by dry etching encountered in top-down methods. InGaN lamellae technology is particularly interesting because by varying the indium content in InGaN lamellae, InGaN quantum wells emitting red, green, and blue light can be grown on such lamellae at low strain levels.

[0008] US2022246797A1 discusses a method for fabricating an InGaN semiconductor template, comprising growing an InGaN pyramid with a tilted surface on a semiconductor substrate; processing the pyramid by removing semiconductor material to form a truncated pyramid with a first upper surface; and growing InGaN on the first upper surface to form an InGaN template layer having c-plane crystal faces constituting the top surface. This InGaN semiconductor template is suitable for further fabrication of semiconductor devices, such as microLEDs configured to emit red, green, or blue light.

[0009] In Gustafsson, Bi, and Samuelson’s “From InGaN pyramids to micro-LEDs characterized by cathodoluminescence”, March 1, 2021, Nano Express 2(1), the authors present a study of the optical properties of each step in a method for fabricating μ-LEDs based on quantum wells embedded in micron-sized InGaN lamellae. In this study, the focus is on structures for red emission, but the technique is also applicable to blue and green emitting μ-LEDs, which are less technically challenging. The starting point is the growth of an InGaN pyramid with a hexagonal substrate of submicron size. The pyramid is planarized to produce a flat top c-face for subsequent InGaN quantum well growth. The planarized wafer serves as a template for growing low-strain single quantum wells in heterostructures and full-LEDs.

[0010] Summary of the Invention The proposed solution relates to apparatus and methods as outlined in the independent claims. Additional aspects and features are summarized below and are at least partially set forth in the dependent claims.

[0011] According to a first aspect of this disclosure, a semiconductor structure for microLEDs is provided. The structure comprises an epitaxial wafer and a plurality of InGaN wafers grown through mask openings of the epitaxial wafer. The InGaN wafers include quantum well layers, which may contain a plurality of quantum wells. Optionally, each InGaN wafer has a top c-face surface that can be connected to a driving circuit to generate light emission. The quantum well layer may be formed in the InGaN wafer and may be sandwiched between two InGaN layers, such as a lower n-InGaN portion and an upper p-InGaN portion. The quantum well layer can be configured at a height in the InGaN wafer that is related to the emission wavelength.

[0012] The proposed solution is based on the inventors’ research, which showed that when the quantum well layer is formed closer to the top portion of the pyramid (where the diameter is also smaller), the quantum well grows thicker and may also have a higher concentration of indium, meaning that its emission is shifted to a longer wavelength.The proposed solution thus involves the fabrication of microLEDs for emitting a certain wavelength, configured through careful selective epitaxial growth of quantum well layers at a certain height. Specifically, this is used for monolithic growth of RGB triplets from a common epitaxial wafer, wherein InGaN wafers having quantum well layers at different heights at least partially determine the emission color.

[0013] InGaN wafers can be arranged in groups on the epitaxial wafer for red, green, and blue light emission. InGaN wafers can be arranged in a triangular pattern, and InGaN wafers configured for emission of the same color can be arranged in a hexagonal pattern. InGaN wafers can be arranged in groups configured for different emission wavelengths, and the emission wavelength of the InGaN wafers can be increased with increasing spacing within the group. An InGaN wafer configured to emit red light may have a base layer of InGaN with a first indium concentration adjacent to the epitaxial wafer, and a buffer layer of InGaN with a second indium concentration higher than the first indium concentration between the base layer and the quantum well layer.

[0014] According to a second aspect of this disclosure, a method for manufacturing a semiconductor structure for a microLED is provided. The method includes epitaxially growing an InGaN pyramid through a mask window of an epitaxial wafer, for example, truncating the InGaN pyramid by etching or annealing to form a truncated InGaN pyramid, and growing a separate quantum well layer on the truncated pyramid to form a separate InGaN wafer. The originally grown InGaN pyramid may be grown simultaneously with a common composition and thus have the same indium concentration. The truncated pyramid (which includes the remainder of the truncated original grown pyramid) forms a corresponding base layer for forming the respective and separate monolithically grown InGaN wafers. Optionally, the method may include growing a buffer layer on each substrate layer prior to growing a quantum well layer. The indium concentration of the respective buffer layer can be customized for the emission color of the respective InGaN wafer. A selective mask of the InGaN wafer can be used for the epitaxial growth of the quantum well layer and optional buffer layer for emission in one of the wavelength regions of red, green, and blue. The growth of the quantum well layer can be performed at a height on the epitaxial wafer associated with the desired emission wavelength. The formation of quantum well layers on the InGaN wafer for different emission wavelengths can be performed in common epitaxial processes.

[0015] The proposed solution thus provides a semiconductor structure having multiple InGaN wafers monolithically grown from a common epitaxial wafer, wherein the InGaN wafers can be used to form RGB pixels. The proposed solution further provides a microLED device comprising a semiconductor structure connected to a driving circuit.

[0016] The proposed solution offers significant advantages over prior art solutions. In prior art LED growth, monochromatic LEDs of blue, green, or red can be fabricated on a single wafer (or in a single growth run). To fabricate a full-color microLED display, mass transfer is required to transfer the subpixels of the R, G, B microLEDs. This is a very challenging step, especially impractical for microLEDs smaller than 10 μm. In contrast, the proposed solution provides RGB subpixels by continuously growing them on the same wafer. Thus, each full RGB pixel containing three R / G / B subpixels can be directly bonded to the driving circuit, avoiding the need for mass transfer. This provides monolithic integration of RGB wafer microLEDs via epitaxial methods such as metal-organic chemical vapor deposition (MOCVD).

[0017] Brief Description of the Drawings Figure 1 schematically illustrates three epitaxially grown semiconductor structures in the form of a hexagonal InGaN pyramid, upon which various embodiments of the proposed solution can be obtained.

[0018] Figure 2 schematically illustrates an example of an InGaN wafer with a single quantum well according to one embodiment.

[0019] Figure 3 schematically illustrates an example of a single quantum well sandwiched between two InGaN layers with low indium content and close to the top c-face, according to one embodiment.

[0020] Figure 4 schematically illustrates a first example of a process flow for fabricating red, green, and blue InGaN wafers on the same epitaxial wafer (i.e., from the same growth layer) according to the proposed solution.

[0021] Figure 5 schematically illustrates a second example of a process flow for fabricating red, green, and blue InGaN wafer LEDs on the same epitaxial wafer.

[0022] Figure 6 schematically illustrates an InGaN wafer composition for RGB growth according to an example of the proposed solution.

[0023] Figure 7 illustrates an example of the proposed solution, including a center-to-center spacing design of the growth mask apertures on the epitaxial wafer for locally adjusting the growth rate and the resulting emitted light color.

[0024] Figure 8A shows a top view of the arrangement of contacts on a semiconductor structure for attachment to a driving circuit according to an example.

[0025] FIG8B schematically shows a side view of the contact to the semiconductor structure according to an example.

[0026] FIG8C schematically shows a semiconductor device according to an example, wherein the semiconductor structure is connected to a driving circuit to generate RGB light emission.

[0027] FIG9 schematically shows a hexagonal InGaN RGB wafer array design according to an embodiment. Specification 3 / 14 pages 6 CN 121866871 A

[0028] FIG10A shows a first example of RGB pixels based on the pattern of FIG9.

[0029] Figure 10B illustrates a second example of RGB pixels based on the pattern of Figure 9.

[0030] Figure 11 shows an exemplary pixel array layout of a display based on the example of Figure 10A.

[0031] Detailed Description of the Invention The detailed description set forth below provides information and examples of the disclosed technology with sufficient detail to enable those skilled in the art to implement this disclosure.

[0032] Ternary InGaN alloys are widely used as active layers (or quantum wells) in nitride LEDs and laser diodes. The thickness of the InGaN active layer is typically no more than 3 nm, primarily to confine the effects of the quantum confined Stark effect (QCSE), which reduces the spatial overlap between the electron and hole wave functions in the quantum well. Another reason is that when the layer is grown thicker, the crystal quality of InGaN can deteriorate rapidly, partly due to the large miscibility gap between GaN and InN, but mainly due to the strain effects from growth on a mismatched substrate. However, the prospect of using thick and relaxed InGaN films as substrates for nitride optoelectronic devices is highly desirable, where high indium content InGaN active layers are required.

[0033] Selective region growth has been widely used to fabricate GaN to reduce dislocation density caused by lattice mismatch between the substrate and the epitaxial GaN layer. If the mask aperture is made small enough, such as 200 nm or smaller, dislocation-free GaN structures including nanowires and pyramids can be grown.

[0034] Figure 1 shows three epitaxially grown semiconductor structures in the form of hexagonal InGaN pyramids, which can be used as the basis for various embodiments of the proposed solution. The figure shows a semiconductor structure that, according to the proposed solution, can be fabricated and used as a starting structure for fabricating InGaN wafers. For example, a sapphire or Si base substrate 1 is provided with one or more layers of c-oriented GaN as a growth layer 2, such as a (0001) oriented GaN film. For example, a mask layer 3 of SiNx is formed on top of the GaN layer. Holes (or windows / or apertures) 4 are provided in the mask layer. Holes 4 can be fabricated using various types of photolithography, such as EBL (electron beam lithography), nanoimprint lithography, DUV (deep ultraviolet) lithography, etc. The aperture 4 can be very narrow, for example, having a diameter of 20–200 nm, 50–150 nm, or 60–100 nm. Optionally, a seed crystal of a Group III nitride material (such as GaN) can be grown. In a subsequent step, a hexagonal pyramid 5 of InGaN is epitaxially grown on the aperture from the growth layer (optionally from the seed crystal). Growth occurs where gallium and indium compounds diffuse primarily from the SiN mask surface to the aperture, without any nucleation on the mask surface. Thus, the growth of InGaN pyramids with a composition of up to 20% indium has been achieved, as determined by photoluminescence (PL) measurements.The growth of InGaN pyramids can be carried out with selective doping, resulting in negatively doped n-InGaN pyramids 5. Various examples and aspects related to the prefabrication of the structure of FIG1 are disclosed in WO2020187986A1, which is incorporated herein by reference.

[0035] Hexagonal InGaN pyramids with a diagonal base size of several hundred nanometers (e.g., >400 nm) can be used. These pyramids have {101̅1} lateral faces and occasionally small flat (0001) top faces. Each pyramid is a homogeneous InGaN semiconductor structure. In some instances, one or more pyramids can be epitaxially grown in two or more epitaxial stages with different (e.g., increasing) indium concentrations, as will be described.

[0036] Prefabrication steps of epitaxial growth from mask holes yield InGaN pyramids with no or substantially no dislocations. As a result, emission inhomogeneities caused by dislocations between pixels (individual semiconductor devices) are avoided. This contributes positively to achieving high quantum efficiency, such as greater than 10%. Furthermore, very thin (e.g., less than 1 μm) GaN buffer / growth layers 2 can be used, resulting in very low wafer bending. This provides the benefit of high-yield processing.

[0037] Various aspects of the proposed solution are based on creating quantum wells (QWs) embedded within InGaN pyramids or truncated InGaN pyramids to obtain InGaN wafers configured to operate as microLEDs, each microLED configured to emit one of red, green, and blue light. In some embodiments, each such InGaN wafer (i.e., for each color) is processed from the same InGaN pyramid array on page 4 / 14 of the basic specification 7 CN 121866871 A by simultaneous growth from corresponding mask apertures in an epitaxial process.

[0038] According to some aspects, the InGaN pyramids are arranged / grown on a carrier in a first triangular pattern, wherein each InGaN wafer has six adjacent InGaN wafers at equal distances. This achieves uniformity in the growth of the InGaN pyramids, upon which InGaN lamellae are formed. In such embodiments, the RGB triplets can be defined, for example, in a straight line or in a triangular arrangement.

[0039] Using epitaxially grown InGaN pyramids, grown from a small aperture to a common growth layer, provides the advantages of high crystal quality and high fabrication efficiency for InGaN lamellae.

[0040] According to some examples, the pyramidal shape of the starting structure is advantageously used based on the understanding that truncating to produce a top c-face with different truncated pyramid heights (i.e., at different elevations on the carrier or epitaxial wafer) will also provide a basis for preparing QWs that emit light at different wavelengths (different colors) in relation to the surface dimensions of the c-face. This example provides the possibility of growing QW layers of all three colors (each QW layer containing one or more QWs and associated layers) in a common growth process step.

[0041] According to some examples, pre-arranging individual InGaN pyramids for each pixel according to the growth mask provides an efficient basis for individually masking or not masking the selected pyramids, thereby removing material or epitaxially growing the selected InGaN wafers to produce InGaN wafers that emit light in the desired wavelength (e.g., red, green, or blue).

[0042] According to some examples, the pyramids can be configured with a custom pattern defined by the arrangement of mask holes on the epitaxial wafer. In some instances, the pattern may define groups of pixels of the same color (i.e., configured to emit light of the same color), with pre-configured pixel spacing within the groups, wherein the pixel spacing varies depending on the color. Specifically, the pixel spacing PP (e.g., center-to-center distance of a mask aperture) within each group is pre-configured to facilitate different growth of QW layers for different color groups. Thus, two or three groups of QW layers can be grown simultaneously in the same epitaxial process.

[0043] Figures 2 and 3 show different types of InGaN wafers, i.e., InGaN pyramids, which have been truncated and subjected to subsequent epitaxial growth to form QW layers and upper p-InGaN growth, according to various instances of the proposed solution.

[0044] Figure 2 shows an example of an InGaN wafer 100 comprising a QW layer 110 having a single QW, according to one embodiment. The InGaN wafer 100 has a truncated pyramid shape with a substantially flat top surface 120. The InGaN wafer 100 is fabricated from a pyramid grown onto growth layer 2 through a mask window, and a portion thereof is shown. A QW layer 110 is formed in the InGaN wafer 100 and configured at a height related to the expected emission wavelength. The figure shows an example of an InGaN wafer with a single QW sandwiched between two InGaN layers with lower indium content. The light emission from the QW is approximately 620 nm.

[0045] Figure 3 shows an example of an InGaN wafer 100 with a QW layer 110 comprising a single QW sandwiched between two InGaN layers with lower indium content and close to the top c-face. Compared to Figure 2, due to the thicker QW and higher indium content, the light emission from the QW has shifted to 750 nm, indicating that for fixed growth conditions, the emission wavelength can be shifted depending on the distance to the tip / vertices of the pyramid.

[0046] The proposed solution includes a method for manufacturing a semiconductor device comprising InGaN wafers configured for red, green, and blue (RGB) emission on the same carrier, which is a common semiconductor substrate, also referred to herein as an epitaxial wafer. Each InGaN wafer is thus configured to operate as a microLED when connected to a driving circuit.

[0047] High efficiency is provided by minimizing the risk of damaging the remaining material of the pixel by employing bottom-up growth instead of using prior art plasma etching to remove InGaN material to form InGaN mesas of a certain pixel size. Specification 5 / 14 pages 8 CN 121866871 A

[0048] Figure 4 presents the various stages of a first example of a process flow for manufacturing red, green, and blue InGaN wafers 100 on the same epitaxial wafer 10 according to the proposed solution. The process includes, or succeeds, epitaxial growth of InGaN pyramids 5 through mask apertures 4 of the epitaxial wafer 10. In this case, it can be noted that the epitaxial wafer 10 (or carrier) at least includes a mask layer 3, while the underlying growth layer 2 for growing the InGaN pyramid through the mask holes can be removed or thinned after the InGaN wafer is completed.

[0049] This process involves truncating the InGaN pyramid to form a truncated InGaN pyramid and growing a QW layer to form a truncated InGaN wafer 100 (100B, 100G, 100R). In the case of the proposed solution, one or more of various types of processes for material removal or rearrangement can be used to obtain the truncated pyramid shape. Etching is one example, while chemical mechanical polishing (CMP) is another.

[0050] The top image depicts an InGaN pyramid with a specific indium content (e.g., 8-12%, e.g., 10%). This may correspond to Figure 1. The intermediate image shows the result after progressive truncation to define a group of three truncated pyramids 40B, 40G, 40R with exposed top c-faces at three different truncation heights, i.e., with exposed c-faces at different elevations above the carrier (e.g., above the top surface of mask layer 3). Truncation involves material removal, such as by back-side etching, annealing, or polishing.

[0051] In some instances (as will be described with reference to Figures 5 and 6), this involves truncating all pyramids to leave a corresponding substrate layer with a common height (e.g., 80–120 nm, or approximately 100 nm) on the top surface of the carrier. An additional buffer layer can then be grown on the corresponding substrate layer. This provides an improvement in the surface of the upper c-face prior to QW growth. The indium concentration of the buffer layer can be customized according to the desired emission color.

[0052] The intermediate image thus shows a set of three truncated pyramids 40B, 40G, 40R with exposed top c-faces at three different cut-off heights, i.e., exposed c-faces at different elevations above the carrier (e.g., above the top surface of mask layer 3). In this document, all wafers are thus processed to expose c-faces at three different heights; the truncated pyramid 40B with height hB is configured to form a QW layer for blue emission, the truncated pyramid 40G with height hG is configured to form a QW layer for green emission, and the truncated pyramid 40R with height hR is configured to form a QW layer for red emission.

[0053] Quantum well layers 111, 112, 113 can then be epitaxially grown in a single step on the truncated InGaN pyramids 40B, 40G, 40R with different height / top c-face dimensions, intended to have RGB microLEDs fabricated in a co-epitaxy process. In other words, for all colors RGB, the same formulation can be used to prepare the layers included in the QW, including the additional InGaN top layer above the QW, which saves processing time.

[0054] To achieve the structure of the intermediate image of FIG4, based on the structure of the top image, a protective layer of resist or other dielectric material can first be deposited on the sample surface (the top surface of the epitaxial wafer 10 and the pyramid 5). In some instances, the resist / dielectric protective layer is selected to have a dry etching rate similar to that of the InGaN material, such as crystalline Al2O3. After depositing the protective layer, the surface can be slightly wavy, following the shape profile of the pyramid. CMP can be used to planarize the protective layer.

[0055] According to some instances, when the buffer layer is not included, another layer of other type of resist / hard mask can be deposited on the prepared surface for photolithography, and the resist / hard mask can be patterned such that a set of apertures is created on the top 1 / 3 of the InGaN pyramid. Subsequently, dry etching can be performed to truncate the InGaN pyramids exposed below the aperture to form the top c-face for a monochrome microLED (e.g., blue). Selective masking is a known procedure and therefore will not be described or shown in detail.

[0056] In one example, the process can continue by removing the top resist / hard mask and subsequently depositing a resist / dielectric layer again to cover the truncated pyramids. By repeating the above procedure twice from a CMP, two additional sets of truncated pyramids with different heights can be prepared for two other colors of microLEDs (green and red). After removing all resist material, the structure shown in the intermediate image of Figure 4 is obtained.

[0057] In another example, the first step of etching the top 1 / 3 of the InGaN pyramid can be followed by a step of removing the resist to form apertures on a second set of pyramids, wherein etching can be performed on both the first and second sets of pyramids. Finally, after all three pyramids have been etched, the remaining pyramids can also be exposed. According to the middle image of Figure 4, the selected time for these three process steps can be configured to obtain the corresponding pyramids to three different selected cut-off heights.

[0058] In the example where all pyramids are first etched on the back side to form the corresponding substrate layer, a selective masking process can alternatively be used to grow the buffer layer.

[0059] To conclude the template preparation, the resist / hard mask and protective layer are removed, and the sample is cleaned for subsequent epitaxy.

[0060] Corresponding to the middle image of Figure 4, the fabricated sample can be loaded back into the MOCVD chamber for epitaxy of QW layers 111, 112, and 113. Each QW layer can contain an n-type InGaN buffer layer, an InGaN QW, a GaN or AlGaN electron blocking layer, and a p-InGaN layer. The smaller the top c-face during QW layer growth, the higher the indium content can be obtained in the InGaN QW. By adjusting the top c-face dimensions of these three sets of truncated pyramids 40B, 40G, and 40R (i.e., by configuring the height of the truncated pyramids) and growth conditions, InGaN QWs emitting blue, green, and red light can be obtained in a single epitaxial growth process. In this case, it should be noted that each pyramid can undergo epitaxy to grow more than one QW per pyramid.

[0061] The bottom image of Figure 4 shows the result after a single epitaxy on all truncated InGaN pyramids 40B, 40G, 40R, resulting in InGaN wafers 100B, 100G, 100R with corresponding QWs 111, 112, 113 located at three different heights and configured to emit three different colors, namely blue, green, and red. It should be noted that a single epitaxy refers to performing the same series of epitaxial growth steps on all truncated pyramids 40B, 40G, 40R.

[0062] As shown in the bottom image, the QW layer growth process also includes the additional growth of an upper InGaN layer (such as doped p-InGaN). In some instances, the growth of the upper InGaN layer continues to the full pyramid shape of each corresponding wafer. Thereafter, all wafers are truncated, for example by annealing, etching, or polishing, to obtain the same height for all InGaN wafers. This provides a simplified final process and also achieves a uniform InGaN height, which simplifies contact with the driving circuitry.

[0063] Figure 5 shows another example of a process flow for fabricating red, green, and blue InGaN wafer LEDs on the same epitaxial wafer 10.The process flow includes the epitaxial growth of a QW layer for selectively masking InGaN wafers to emit in one of the red, green, and blue wavelength regions.

[0064] The process is based on creating QWs of different colors at equal truncated c-plane heights (i.e., substrate layers) covering the selected wafers, and performing epitaxial growth on the remaining exposed wafers in three consecutive steps to form R, G, and B LEDs.

[0065] A) A pyramid of n-InGaN with a specific indium content (e.g., 8-12%) is depicted. This may correspond to Figure 1.

[0066] B) An InGaN pyramid is shown planarized / truncated to the same height (leaving the substrate layer). In this figure, each truncated pyramid 51 is surrounded by an additional spacer layer 52 of the same height. The spacer layer 52 is a dielectric material or at least an inorganic material (not a resist polymer) because it needs to withstand high temperatures without degrading and contaminating the InGaN. In various embodiments, spacer layer 52 comprises SiNx, Al2O3, TiN, or other suitable materials.

[0067] C) shows the addition of growth mask 53 material to selected 2 / 3 of all truncated pyramids, followed by epitaxial growth of an LED structure comprising a QW layer 111 intended for one color (e.g., blue light emission), optionally preceded by the growth of a buffer layer tailored for blue light emission, such as having an indium concentration of 5-10%, which further provides the benefit of reducing any possible tail absorption of QW light. The growth mask material may, for example, comprise Al2O3 or SiNx by atomic layer deposition (ALD).

[0068] In other words, after the InGaN pyramids are truncated using dry etching or CMP to form the structure in B), the sample surface is covered with a layer of growth mask material. A set of truncated pyramids is exposed by photolithography and dry etching for subsequent epitaxy of a QW layer (optionally with a buffer layer grown prior to this) and an upper p-InGaN layer to form a microLED 100B configured to emit a color (e.g., blue).

[0069] D) shows the previously grown LED structure 100B covered in a growth mask material (i.e., by covering the entire sample again with a mask layer, such as ALD Al2O3 or SiNx), and half of the remaining truncated pyramids exposed by photolithography and dry etching, followed by epitaxial growth of an LED structure containing a QW layer to form a microLED 100G configured to emit a second color (e.g., green light emission).

[0070] E) shows the previously grown LED structure covered in a growth mask, exposing the remaining truncated pyramids, followed by epitaxial growth of an LED structure 100R having a QW intended for a final color (e.g., red light emission).

[0071] In this example, for each color of the pixel, a separate formulation for epitaxy can be used to generate—in particular—the QW and buffer layer. This provides greater operational freedom for the configuration of InGaN wafers for different colors of microLEDs. This example thus truncates all InGaN pyramids in the same manner, and then performs three epitaxial growths aimed at obtaining blue, green, and red microLEDs on selected sets of truncated pyramids, while other sets of truncated pyramids are covered with mask material.

[0072] Figure 6 shows the composition of an InGaN wafer for RGB growth according to an example of the proposed solution. The InGaN wafer has a substrate layer 61 adjacent to the surface 11 of the epitaxial wafer (such as the top surface of the mask layer 3). As mentioned above, the substrate layer 61 can be the remainder of the original pyramid 5 after truncation. The substrate layer size, which is substantially equal to the size of the original pyramid substrate, can be in the range of 700-900 nm, such as the point-to-point distance of its hexagonal shape being approximately 800 nm. The substrate layer is made of InGaN (n-InGaN) with a first indium concentration, such as about 10% or 8-12%, and can be about 100 nm high or 80-120 nm high. A buffer layer 62 is formed between the substrate layer 61 and the QW layer 110, wherein the buffer layer 62 is made of InGaN with a second indium concentration, which may be different from the first indium concentration.

[0073] For an InGaN wafer 100R configured to emit red light, the buffer layer 62R may be made of InGaN with a second indium concentration (e.g., 18-20%) higher than the first indium concentration. The buffer layer can be grown to obtain a c-plane surface at a height of about 520-550 nm from the surface of the epitaxial wafer.

[0074] According to various embodiments, in order to minimize lattice stress and defect generation, the n-type bottom wafer segment (i.e., the substrate 61 where the pyramid is closest to the mask layer) is designed to have an In composition corresponding to a bandgap emission of 420-430 nm. For the red emitting LED 100R, a 475 nm light-emitting buffer layer 62R is grown before the QW layer 110, while the 425 nm light-emitting layer can be used for green and blue. This suppresses defect formation.

[0075] In some instances, in the formation of the green 100G and blue 100B microLEDs, no buffer layer is grown, or a buffer layer with the same indium concentration as the substrate layer 61 is grown.

[0076] However, in other instances, InGaN (n-InGaN) buffer layers 62G and 62B are also grown on the substrate layer 61 to form InGaN wafers for green 100G and blue 100B emission.

[0077] For the green InGaN wafer 100G, a buffer layer 62G is formed between the substrate layer 61 and the QW layer 110, wherein the buffer layer 62G is made of InGaN with a second indium concentration that is the same as or higher than the first indium concentration, such as 10-15%. The buffer layer can be grown to obtain a c-plane surface at a height of approximately 360-400 nm from the surface of the epitaxial wafer.

[0078] For the blue InGaN wafer 100B, a buffer layer 62B is formed between the substrate layer 61 and the QW layer 110, wherein the buffer layer 62B is made of InGaN with a second indium concentration that is the same as or lower than the first indium concentration, such as 5-10%. The buffer layer can be grown to obtain a c-plane surface at a height of approximately 240-280 nm from the surface of the epitaxial wafer.

[0079] For each InGaN wafer 100R, 100G, 100B, a further growth of upper InGaN layers (p-InGaN) 63R, 63G, 63B is performed above the QW layer 110. As described, when the initial substrate layer 61 size is in the range of 700-900 nm, such as approximately 800 nm dot-to-dot spacing, the overall total height of each InGaN wafer can be in the range of 720-770 nm. According to measurements, after the growth step, the substrate of the corresponding InGaN wafer can be increased to 900-960 nm.

[0080] Figure 7 shows an example of the proposed solution, including a center-to-center spacing design of the holes 4 in the growth mask 3 for locally adjusting the growth rate of the epitaxial wafer 10. The figure schematically shows a top view of the mask layer 3. The holes 4 in the mask layer 3 for growing InGaN wafers are configured in groups for red, green, and blue light emission, respectively. This implementation is based on the understanding that the emission wavelength of InGaN wafers increases with increasing spacing within the group.

[0081] According to this implementation of the proposed solution, R, G, and B LEDs are thus fabricated using localized aperture spacing variations. With this configuration, a single-step epitaxial process can be optionally used for QW layer formation and top layer growth.

[0082] In this case, the proposed lattice design is based on the concept that for selective regional growth of InGaN, indium incorporation depends on the spacing between apertures 3. In the figures, this spacing is referred to as the pixel spacing PP. At a spacing of up to 2 μm or greater, growth is controlled by diffusion of adsorbed atoms on the mask surface. All adsorbed atoms falling on the mask surface will diffuse to the nearest InGaN pyramid and contribute to growth there. Thus, growth with a larger spacing implies a locally higher growth rate, resulting in increased indium content (i.e., pre-configuration for longer wavelengths).By carefully designing the spacing between the apertures 4, and thereby designing the pyramids growing from the growth layer 2 through the apertures 4, and by adjusting the growth conditions, InGaN pyramids 5 can be grown in a single epitaxial run (and subsequently truncated and processed to introduce a QW layer), where the indium composition (concentration) is tailored to the target emission wavelength (i.e., blue, green, and red light) based on the spacing between the mask apertures. In this case, a larger spacing provides InGaN growth suitable for longer wavelength InGaN wafers (i.e., towards red). It can be noted that the customized lattice pattern for this purpose can be achieved through the patterning design of the mask apertures 4 in the mask 3 above the growth layer 2. Grouped triangular apertures with a larger c-c distance (pixel spacing between InGaN wafers of the same color) promote higher indium incorporation and longer wavelength emission. Thus, designs with three different c-c spacings will yield red, green, and blue wafer LEDs on the same wafer.

[0083] Figures 8A and 8B schematically illustrate the contacts of the semiconductor structure 80 according to the proposed solution, while Figure 8C shows a microLED device 800, wherein the semiconductor structure 80 is connected to a driving circuit. Without the inclusion of reference numerals in Figures 8, it should be noted that they refer to details highlighted in other figures.

[0084] Figure 8A shows a top view of an example of a triangular arrangement of RGB microLEDs, wherein n-contacts are centrally configured in the triangular pixel arrangement. Individual n-contacts to the respective microLEDs are another option.

[0085] Figure 8B schematically illustrates an example of a semiconductor structure 80 according to the proposed solution. As described and illustrated herein, the semiconductor structure 80 comprises an epitaxial wafer 10, wherein a plurality of InGaN wafers 100 are grown through mask apertures 4 of the epitaxial wafer 10, each InGaN wafer comprising a QW layer 110 containing one or more QWs. The InGaN wafers 100 have a truncated pyramidal shape. Each InGaN wafer is configured to emit one color in RGB and is designated as 100B, 100G, 100R. In this figure, the buffer layer 2 is still retained, but this layer may be peeled or thinned before or after contact.

[0086] A contact spacer layer 81 may be applied to the InGaN wafers 100B, 100G, 100R, wherein p-contacts 82B, 82G, 82R to the respective InGaN wafers protrude through the contact spacer layer 81 and are bonded to the respective top c-surface surface of the InGaN wafers 100B, 100G, 100R. The contact spacer layer 81 is a dielectric layer that allows leads (not shown) to be applied to the p-contacts on the surface of the microLED device as per specification page 9 / 14, CN 121866871 A. n-contacts 83 (or individual contacts) for pixel groups are formed to extend from the base-side surface of the pyramid to the top c-surface side to facilitate connection of the driving circuitry.According to the example shown, the n-contact 83 can be a metallic connection.

[0087] FIG8C schematically illustrates a microLED device 800 comprising a semiconductor structure 80 according to the proposed solution. The figures indicate the attachment and connection of the semiconductor structure 80 to the driving circuit 84. Each InGaN wafer 100R, 100G, 100B has a top c-surface surface that can be connected to the driving circuit 84 by means of corresponding connectors 82R, 82G, 82B to generate light emission.

[0088] The driving circuit 84 is exemplified here as a Si CMOS driving circuit. In some instances, a thin-film active transistor driver may be used alternatively or additionally. Although the top image of FIG8A shows a triangularly formed group of RGB pixels with a central n-contact, the lower image shows a line drawing for simplicity. Either is possible.

[0089] When the microLED device 800 is configured to emit light through the substrate side of the InGaN wafer, the p-contacts 82B, 82G, 82R connected to the upper c-face of the respective InGaN wafer can be reflective to improve light output.

[0090] The substrate 1 is removed (see FIG. 1). As described, the original GaN growth layer 2 can be further thinned or stripped. The epitaxial wafer 10 of the microLED device 800 thus includes a mask layer 3 and optionally includes a portion of the growth layer 2.

[0091] FIG. 9 shows an example of an InGaN RGB wafer array design according to some examples of the proposed solution. The epitaxial growth of the InGaN wafers from holes arranged in a triangle in the growth mask and subsequently forming QWs (where each InGaN wafer has six adjacent InGaN wafers at a common distance) provides very uniform growth conditions and achieves well-controlled composition.

[0092] As shown, a hexagonal array is configured for each color. The hexagonal pattern specifies that the same distance / spacing is configured between all InGaN wafers prepared for the same emission wavelength. This is beneficial for growth uniformity. Specifically, by maintaining the triangular symmetry (and spacing between the centers) of the red, green, and blue wafer LEDs, the color purity and uniformity of each LED color on the wafer are very high.

[0093] Figure 10A shows an example of a pixel group configuration in which triplets of RGB InGaN wafers are combined in a pixel group, enabling any color in the visible spectrum. In this example, triangular pixel groups are configured.

[0094] Figure 10B shows as an example an alternative arrangement of triplets of RGB InGaN wafers in a pixel group, enabling any color in the visible spectrum. In this example, linear combinations are configured.

[0095] Figure 11 shows an example of multiple pixel RGB groups, each containing triplets according to the example of Figure 10A. The pixel array layout illustrates the arrangement of InGaN wafers 100 for red, green, and blue light emission in display applications.

[0096] The above embodiments provide examples of proposed solutions for semiconductor structures and manufacturing methods of microLEDs. The disclosed techniques minimize defects in crystal formation and improve the external quantum efficiency of microLEDs with pixel sizes below 10 μm. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this disclosure. Various modifications and adaptations can be made by those skilled in the art without departing from the scope of this disclosure as set forth in the appended claims.

[0097] Referring to the above description of the proposed solutions and their examples and embodiments, various further related features and examples are summarized below.

[0098] The growth of InGaN pyramids through the mask window 4 of the epitaxial wafer 10 enables the formation of InGaN wafers 100 with specific shapes and configurations. This controlled growth process contributes to the overall quality and performance of the resulting microLEDs because it allows the formation of InGaN wafers with minimal defects and optimized external quantum efficiency.

[0099] The growth mask 3 configured for growing the InGaN pyramids is preferably a dielectric material such as Al2O3, SiNx, or TiN. The holes 4 passing through the openings of the dielectric growth mask are preferably arranged in a triangular lattice, as shown in Figures 9-11, wherein the hole size is in the range of 20-200 nm and spaced 0.5-10 μm apart. Specification 10 / 14 pages 13 CN 121866871 A

[0100] The grown InGaN pyramids 5 are preferably grown as n-type InGaN. The n-type InGaN pyramids can be, for example, doped with Si to a level of 1-5 × 10¹⁸ cm⁻³.

[0101] According to some examples, InGaN pyramids 5 having the same composition are simultaneously grown as n-type InGaN pyramids with a specific indium concentration, wherein the pyramids are subsequently processed to obtain individual RGB InGaN wafers.

[0102] According to other examples, for blue LEDs, GaN or InGaN pyramids (wavelength <380 nm) with an indium content of less than 5% can be used. For green LEDs, an InGaN pyramid with an indium content of approximately 10% (wavelength 420-430 nm) is preferred, and for red LEDs, an indium content of 18%-20% (wavelength 480-500 nm) is preferred. Different indium contents / concentrations can be obtained by growing the InGaN pyramids in separate processes.

[0103] In some instances, for example, as shown with reference to FIG. 6, n-type InGaN may be contained in more than one segment separated in elevation above the epitaxial wafer / mask layer. In some instances, the substrate layer of the InGaN closest to the epitaxial wafer 10 may have the same indium composition as the original InGaN pyramid.However, for the case shown in Figure 6, the fabrication method can begin with an InGaN pyramid emitting 420-430 nm light with an indium content of approximately 10%. After truncating the pyramid, the template can be directly used for blue and green microLEDs. For red microLEDs, a buffer InGaN layer (below the active region of the QW layer) with an indium content of, for example, approximately 18-20% (480-500 nm light) can be grown, followed by the growth of a red InGaN QW to reduce the risk of introducing stacking mismatch boundaries. The variation in indium concentration between the substrate layer and the buffer layer helps to achieve the desired emission wavelength of red light and improve the crystal quality of the InGaN lamellae.

[0104] After the epitaxial growth of the InGaN pyramid, the fabrication method may involve truncating the InGaN pyramid 5 to form a truncated InGaN pyramid (and possibly further InGaN buffer growth). This process helps to produce InGaN wafers 100 with a truncated pyramidal shape, which is advantageous for forming a QW layer at a defined c-plane parallel to the epitaxial wafer and for the overall performance of the microLED.

[0105] When truncating the pyramid 5, a protective layer can be applied before the LED epitaxy, as shown in Figures 4 and 5, prior to the growth of the QW layer (and, where appropriate, the growth of a buffer layer). The protective layer should preferably be deposited using a dielectric material (Al2O3, etc.) similar to the growth mask, as it can be deposited conformally, covering all faces with the same thickness. Other deposition methods typically result in different depositions on different faces.

[0106] The InGaN wafer 100 contains a QW layer, also called an active layer, formed within the wafer, which may itself contain one or more QWs. The QW can be approximately 2–3 nm thick. The compositions (i.e., indium concentrations) used for blue, green, and red are approximately 10–15%, 25–27%, and 35–40%, respectively. For blue and green LEDs, an electron blocking layer (EBL) of AlGaN with an Al content of 10-25% and a thickness of 10-25 nm can be used. For red LEDs, GaN or AlGaN with an Al content of less than 10% can be used as the EBL.

[0107] According to some examples, the QW layer is configured at a height in the InGaN wafer 100 relative to the emission wavelength, as explained and illustrated with reference to FIG4. For at least some of the QW layers, this configuration allows QW layers to be formed on the InGaN wafer 100 for different emission wavelengths in a common epitaxial process or so-called single epitaxy, which simplifies the manufacturing process and reduces manufacturing costs.

[0108] In some examples, the manufacturing method may also include selectively masking the InGaN wafer 100 to epitaxially grow a QW layer for emission in one of the red, green, and blue wavelength regions.This selective masking process enables the creation of semiconductor structures with InGaN wafers configured for different emission wavelengths individually and specifically, allowing the formation of microLEDs capable of emitting red, green, and blue light.

[0109] In some instances, the selective masking process can be performed using various techniques such as photolithography, electron beam lithography, or nanoimprint lithography to produce a desired mask pattern on the epitaxial wafer 10. The mask material can be selected based on its compatibility with the chosen mask technology and its ability to withstand epitaxial growth processes without degradation or causing undesirable contamination of the InGaN material. The use of selective masking for wavelength region emission in the fabrication method of semiconductor structures for microLEDs provides several advantages. By enabling the formation of InGaN wafers 100 with different emission wavelengths on the same epitaxial wafer 10, the selective masking process allows the creation of microLEDs capable of emitting a full range of colors for display applications. Furthermore, selective masking processes can help improve efficiency by optimizing growth conditions for each color and ensuring uniformity of the epitaxial growth process, resulting in InGaN wafers 100 with fewer defects and higher external quantum efficiency. Additionally, combining selective masking processes with co-epitaxial processes can help simplify fabrication methods and reduce overall processing time and cost associated with fabricating semiconductor structures for microLEDs.

[0110] In some instances, the InGaN wafers may contain additional layers with different indium concentrations to further optimize their performance. These additional layers may be located between the substrate layer and the buffer layer, or between the buffer layer and the QW layer. These additional layers can help reduce strain, improve crystal quality, and customize the emission wavelength of the InGaN wafer.

[0111] A p-type InGaN top layer is further grown over the QW layer. For blue LEDs, the p-layer may be p-GaN with a thickness of 100–200 nm or p-InGaN containing only a few percent (<10% or <5%) of In. For green and red LEDs, p-InGaN with indium contents of 10% and 18%, respectively, may be used. p-type doping is achieved using, for example, Mg at levels at least higher than 1 × 10¹⁹ cm⁻³. Rapid thermal annealing can be used to activate the Mg doping.

[0112] As shown in FIG8B, the contact spacer layer 81 can be a polymer. Preferably, a dielectric spacer layer such as PECVD SiOx should be used in conjunction with CMP to expose the top c-face of the p-InGaN layer. Before PECVD SiOx growth, a thin layer of ALD Al₂O₃ can be deposited first to protect the surface from plasma damage at the start of PECVD SiOx deposition and also serves as a surface passivation for the lamellar surface.

[0113] Preferably, as shown in FIG8B, n-type contacts to the substrate end of the InGaN wafer (typically to a growth layer, such as a GaN buffer layer, on the opposite side of the mask layer) and p-type InGaN contacts can be processed on the wafer side of the epitaxial wafer 10, which allows for convenient bonding to driving circuitry, such as a CMOS driver chip. In this case, the flat c-plane top surface of the truncated InGaN wafer provides a surface suitable for bonding p-contacts.

[0114] In one example, the InGaN wafers 100 are arranged in groups on the epitaxial wafer 10 for red, green, and blue light emission. This arrangement enables the fabrication of microLEDs with different emission wavelengths on a single epitaxial wafer 10, which simplifies the manufacturing process and reduces costs.

[0115] In some examples, the InGaN wafers 100 are arranged in groups configured for different emission wavelengths. The emission wavelength of the InGaN wafers 100 increases with increasing spacing within the group. This arrangement allows for tuning the emission wavelength of the InGaN wafer 100 by adjusting the spacing within the group, providing flexibility in designing microLEDs with desired emission wavelengths during InGaN pyramidal growth.

[0116] In various instances, the InGaN wafers 100 are arranged in a triangular pattern. In some instances, the InGaN wafers 100 configured to emit the same color are further arranged in a hexagonal pattern. These patterns provide an efficient arrangement of the InGaN wafers 100 on the epitaxial wafer 10 for red, green, and blue light emission, which helps improve the external quantum efficiency of microLEDs with pixels smaller than 10 μm.

[0117] Overall, the method for fabricating semiconductor structures for microLEDs described herein provides a robust and efficient method for generating high-quality microLEDs with minimal defects in crystal formation and improved external quantum efficiency. The various steps and optional features of this method contribute to the formation of InGaN wafers with precise control over their shape, configuration, and emission properties, ensuring optimal performance of the resulting microLEDs in a wide range of applications.

[0118] Selective masking of wavelength region emission in the manufacturing method of semiconductor structures for microLEDs provides several advantages (see page 12 / 14 of specification, CN 121866871 A). By enabling the formation of InGaN wafers 100 with different emission wavelengths on the same epitaxial wafer 10, the selective masking process allows the creation of microLEDs capable of emitting a full range of colors for display applications. Furthermore, the selective masking process can help improve the efficiency and uniformity of the epitaxial growth process, resulting in InGaN wafers 100 with fewer defects and higher external quantum efficiency.Furthermore, combining selective masking processes with common epitaxial processes can help simplify the manufacturing method and reduce the overall processing time and cost associated with fabricating semiconductor structures for microLEDs.

[0119] The proposed solutions can be configured according to any of the provisions set forth below, depending on the aspects.

[0120] Provision 1. A semiconductor structure for a micro light-emitting diode (microLED) comprising: an epitaxial wafer (10); a plurality of InGaN wafers (100) monolithically grown on the epitaxial wafer, each comprising a quantum well (QW) layer; wherein the plurality of InGaN wafers comprises individual InGaN wafers respectively configured for red, green and blue light emission.

[0121] Provision 2. The semiconductor structure of claim 1, wherein the QW layers are configured at different heights (h) above the surface of the epitaxial wafer in the respective InGaN wafers (100), wherein the height is related to the emission wavelength.

[0122] Provision 3. The semiconductor structure of claim 1 or 2, wherein the QW layer is disposed at an increasing height in InGaN wafers configured for different emission wavelengths in the order of blue-green-red.

[0123] Clause 4. The semiconductor structure of any one of claims 1-3, wherein each InGaN wafer comprises a substrate layer having a first indium concentration adjacent to the epitaxial wafer, and a buffer layer having a second indium concentration between the substrate layer and the QW layer, wherein the second indium concentration is different between InGaN wafers configured for different color emission.

[0124] Clause 5. The semiconductor structure of claim 4, wherein the substrate layer in each InGaN wafer has the same first indium concentration.

[0125] Clause 6. The semiconductor structure of claim 5, wherein the first indium concentration is 8-12%.

[0126] Clause 7. The semiconductor structure of any one of claims 4-6, wherein in InGaN wafers configured for blue emission, the second indium concentration is lower than the first indium concentration.

[0127] Clause 8. The semiconductor structure according to any one of claims 4-7, wherein in the InGaN wafer configured for blue emission, the concentration of the second indium is 5-10%.

[0128] Clause 9. The semiconductor structure according to any one of claims 4-8, wherein in the InGaN wafers configured for green and red emission respectively, the concentration of the second indium is higher than the concentration of the first indium.

[0129] Clause 10. The semiconductor structure according to any one of claims 4-9, wherein in the InGaN wafer configured for green emission, the concentration of the second indium is 10-15%.

[0130] Clause 11. The semiconductor structure according to any one of claims 4-10, wherein in the InGaN wafer configured for red emission, the concentration of the second indium is 18-20%.

[0131] Clause 12. The semiconductor structure according to any of the preceding claims, wherein the InGaN wafer (100) has a truncated pyramidal shape having a top c-face surface connectable to a driving circuit to generate light emission.

[0132] Clause 13. The semiconductor structure according to any of the preceding claims, wherein InGaN wafers (100) configured for the same emission wavelength are arranged in a hexagonal pattern on the epitaxial wafer.

[0133] Clause 14. The semiconductor structure according to any of the preceding claims, wherein the InGaN wafers are arranged in groups of adjacent InGaN wafers on the epitaxial wafer.

[0134] Clause 15. The semiconductor structure according to claim 14, wherein each group comprises a triplet of adjacent InGaN wafers (100) arranged in a triangular pattern. Specification 13 / 14 pages 16 CN 121866871 A

[0135] Clause 16. The semiconductor structure according to claim 14 or 15, wherein each group comprises InGaN wafers (100) configured for blue, green, and red emission.

[0136] Clause 17. The semiconductor structure according to any one of claims 1-15, wherein the InGaN wafers (100) are arranged in groups, the groups being configured for the same emission wavelength, and wherein the spacing (PP) between the InGaN wafers within a respective group is related to the emission wavelength for which the InGaN wafers are configured, such that the spacing increases in the order of blue-green-red.

[0137] Clause 18. A microLED device (800) comprising: a semiconductor structure (80) according to any one of the preceding claims; and a driving circuit (84) connected via p-contacts to a respective top position of each InGaN wafer and via n-contacts to the substrate side of an epitaxial wafer, for generating light emission from the respective InGaN wafer.

[0138] Clause 19. A method for manufacturing a semiconductor structure for a microLED, the method comprising: epitaxially growing an InGaN pyramid (5) through a mask window of an epitaxial wafer (10); truncating the InGaN pyramid to form a truncated InGaN pyramid having a c-face top surface; growing a quantum well (QW) layer on the respective truncated InGaN pyramid; and growing a top InGaN layer on the respective QW layer to form separate InGaN wafers respectively configured for red, green, and blue light emission.

[0139] Clause 20. The method of claim 19, wherein the QW layer is grown at different heights (h) above the surface of the epitaxial wafer in the respective InGaN wafers (100), wherein the height is related to the emission wavelength.

[0140] Clause 21. The method of claim 19 or 20, wherein the QW layer is grown at an increasing height in InGaN wafers configured for different emission wavelengths in a blue-green-red order.

[0141] Clause 22. The method of any one of claims 19-21, wherein the truncated InGaN pyramid forms a corresponding substrate layer having a first indium concentration, the method further comprising: growing a buffer layer having a second indium concentration on the substrate layer prior to growing the QW layer, wherein the second indium concentration is different between InGaN wafers configured for different color emission.

[0142] Clause 23. The method of claim 22, wherein the substrate layer in each InGaN wafer has the same first indium concentration.

[0143] Clause 24. The method of any one of claims 19-23, wherein the growth of quantum well layers on InGaN wafers for different emission wavelengths is performed in a common epitaxial process. Instruction manual, page 14 / 14, 17 CN 121866871 A, Figure 1; Instruction manual, Figure 1 / 11, page 18 CN 121866871 A, Figure 2; Instruction manual, Figure 2 / 11, page 19 CN 121866871 A, Figure 3; Instruction manual, Figure 3 / 11, page 20 CN 121866871 A, Figure 4; Instruction manual, Figure 4 / 11, page 21 CN 121866871 A, Figure 5; Instruction manual, Figure 5 / 11, page 22 CN 121866871 A, Figure 6; Instruction manual, Figure 6 / 11, page 23 CN 121866871 A, Figure 7; Figure 8A; Instruction manual, Figure 7 / 11, page 24 CN 121866871 A, Figure 8B; Figure 8C; Instruction manual, Figure 8 / 11, page 25 CN 121866871 A, Figure 9; Figure 10A; Instruction manual, Figure 9 / 11, page 26 CN 121866871 A Figure 10B Instruction Manual Appendix 10 / 11 Page 27 CN 121866871 A Figure 11 Instruction Manual Appendix 11 / 11 Page 28 CN 121866871 A.

Claims

1. A semiconductor structure (80) for a micro light-emitting diode (microLED), comprising: Epitaxial wafer (10); Multiple InGaN wafers (100B, 100G, 100R) monolithically grown on an epitaxial wafer each contain quantum well (QW) layers (111, 112, 113); The plurality of InGaN wafers include individual InGaN wafers configured for red, green, and blue light emission, respectively. Its features The QW layer is disposed at different heights (h) above the surface of the epitaxial wafer in the corresponding InGaN wafer (100). B h G h R ( ) where the height is related to the emission wavelength.

2. The semiconductor structure of claim 1, wherein the QW layer is disposed at an increasing height in an InGaN wafer configured for different emission wavelengths in a blue-green-red order.

3. The semiconductor structure according to claim 1 or 2, wherein each InGaN wafer comprises a substrate layer (61) with a first indium concentration adjacent to the epitaxial wafer, and a buffer layer (62B, 62G, 62R) with a second indium concentration between the substrate layer and the QW layer, wherein the second indium concentration is different between InGaN wafers configured for different color emission.

4. The semiconductor structure according to claim 3, wherein the substrate layer in each InGaN wafer has the same first indium concentration.

5. The semiconductor structure according to claim 4, wherein the concentration of the first indium is 8-12%.

6. The semiconductor structure according to any one of claims 3-5, wherein in the InGaN wafer configured for blue emission, the second indium concentration is lower than the first indium concentration.

7. The semiconductor structure according to any one of claims 3-6, wherein in the InGaN wafer configured for blue emission, the concentration of the second indium is 5-10%.

8. The semiconductor structure according to any one of claims 3-7, wherein in the InGaN wafers respectively configured for green and red emission, the second indium concentration is higher than the first indium concentration.

9. The semiconductor structure according to any one of claims 3-8, wherein in the InGaN wafer configured for green emission, the concentration of the second indium is 10-15%.

10. The semiconductor structure according to any one of claims 3-9, wherein in the InGaN wafer configured for red emission, the concentration of the second indium is 18-20%.

11. The semiconductor structure according to any one of the preceding claims, wherein the InGaN wafer (100) has a truncated pyramidal shape and a top c-face surface that can be connected to a driving circuit to generate light emission.

12. The semiconductor structure according to any one of the preceding claims, wherein the InGaN wafers (100) configured for the same emission wavelength are arranged in a hexagonal pattern on the epitaxial wafer.

13. The semiconductor structure according to any one of the preceding claims, wherein the InGaN wafers are arranged in a group adjacent to each other on the epitaxial wafer.

14. The semiconductor structure of claim 13, wherein each group comprises a ternary array of adjacent InGaN wafers (100) arranged in a triangular pattern.

15. The semiconductor structure of claim 13 or 14, wherein each group comprises an InGaN wafer (100) configured for blue, green and red emission.

16. The semiconductor structure according to any one of claims 1-14, wherein the InGaN wafers (100) are arranged in groups, the groups are configured for the same emission wavelength, and wherein the spacing (PP) between the InGaN wafers in the respective groups is related to the emission wavelength for which the InGaN wafers are configured, such that the spacing increases in the order of blue-green-red.

17. A microLED device (800), comprising: The semiconductor structure (80) according to any one of the preceding claims; and The driving circuit (84), connected via p-contacts (82B, 82G, 82R) to the respective top position of each InGaN wafer and via n-contacts (83) to the substrate side of the epitaxial wafer, is used to generate light emission from the respective InGaN wafer.

18. A method for manufacturing a semiconductor structure for microLEDs, the method comprising: InGaN pyramids (5) are epitaxially grown through the mask window of the epitaxial wafer (10); The InGaN pyramid is truncated to form a truncated InGaN pyramid (40B, 40G, 40R) with a c-faced top surface; Quantum well (QW) layers (111, 112, 113) were grown on the corresponding truncated InGaN pyramids; and A top InGaN layer is grown on the corresponding QW layer to form separate InGaN wafers (100B, 100G, 100R) respectively configured for red, green, and blue light emission, characterized in that the QW layer is at different heights (h) above the surface of the epitaxial wafer in the corresponding InGaN wafer (100). B h G h R It grows at a height that is related to the emission wavelength.

19. The method of claim 18, wherein the QW layer is grown at increasing height in an InGaN wafer configured for different emission wavelengths in a blue-green-red order.

20. The method of claim 18 or 19, wherein the truncated InGaN pyramid forms a corresponding substrate layer having a first indium concentration, the method further comprising: Before growing the QW layer, a buffer layer (62B, 62G, 62R) with a second indium concentration is grown on the substrate layer, wherein the second indium concentration is different between InGaN wafers configured for different color emission.

21. The method of claim 20, wherein the substrate layer in each InGaN wafer has the same first indium concentration.

22. The method according to any one of claims 18 to 21, wherein the growth of quantum well layers on InGaN wafers for different emission wavelengths is carried out in a common epitaxial process.

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