Optoelectronic device and manufacturing method

Abstract

Title: Optoelectronic device and manufacturing method The invention relates to a method for manufacturing a passive structure (20, 21) for an optoelectronic device, the method comprising: • A formation of a photosensitive layer, • An exposure of the photosensitive layer through a lithography mask comprising at least one mask pattern (11, 12), said exposure being configured to form in the photosensitive layer a diffraction pattern (C) generated by the mask pattern (11, 12), • A formation, from the diffraction pattern (C), of the passive structure (20, 21), the passive structure (20, 21) being arranged around an active part (31, 32) of the optoelectronic device. The invention also relates to an optoelectronic device comprising a passive structure obtained by such a method. Figure for the abstract: Fig. 3.

Description

Title of the invention: Optoelectronic device and manufacturing method Technical field

[0001] The present invention relates to the field of technologies for microelectronics and optoelectronics. It finds a particularly advantageous application in the manufacture of optoelectronic devices comprising in particular light-emitting diodes (LEDs) arranged in cavities, allowing the performance of these devices to be improved. STATE OF THE ART

[0002] The integration of LEDs on a screen or a panel, or even on a PCB type printed circuit substrate (acronym for "Printed Circuit Board"), must respect certain constraints of positioning and spacing between the different LEDs. These constraints can be due to physical phenomena, to avoid optical coupling between pixels for example, or to technical limitations, for example the resolution of the manufacturing equipment.

[0003] This directly impacts the final resolution of an LED-based emissive display. One solution is to use lithography equipment with high resolutions, allowing the positioning of the individual LEDs to be precisely defined and delimited. The spacing between the individual LEDs can thus be reduced. However, the costs associated with this high-resolution lithography equipment are extremely high.

[0004] Furthermore, the use of this type of lithography equipment, which imposes severe constraints on the level of metallic contamination of the plates, is not suitable for carrying out end-of-process steps such as the formation of silver-based reflectors. This type of equipment is also generally not suitable for handling unconventional substrates, i.e. substrates other than silicon-based substrates. The processes related to the use of this type of lithography equipment can also damage certain sensitive elements of the LEDs, for example the color conversion modules (CCMs).

[0005] There is therefore a need for a method for manufacturing LED-based systems with improved resolution while limiting manufacturing costs. Such a method is also preferably versatile and can be implemented on different types of substrates, and / or with different contaminating or thermally sensitive materials. An object of the present invention is to meet these needs by at least partially overcoming the drawbacks of known solutions.

[0006] In particular, an object of the present invention is to propose a method for manufacturing a passive structure, in particular for an optoelectronic device, which can be implemented at low cost, in particular for the manufacture of so-called high-resolution screens. Another object of the present invention is to propose an optoelectronic device obtained by such a manufacturing method.

[0007] Other objects, features and advantages of the present invention will become apparent upon examination of the following description and the accompanying drawings. It is understood that other advantages may be incorporated. In particular, certain features and advantages of the device may apply mutatis mutandis to the method, and vice versa. SUMMARY

[0008] To achieve the above-mentioned objectives, one aspect relates to a method of manufacturing a passive structure on a substrate, the method comprising: • Formation of a photosensitive layer based on a photosensitive resin on the substrate, • An exposure of the photosensitive layer through a lithography mask comprising at least one mask pattern, the exposure being configured to form in the photosensitive layer a diffraction pattern generated by the mask pattern, • A formation, from the diffraction pattern, of the passive structure in the photosensitive layer on the substrate.

[0009] Thus, the method according to the present invention takes advantage of the diffraction phenomena through the lithography mask to form the passive structure on the substrate. The diffraction pattern is naturally well defined, without the need for high-resolution lithography equipment. The diffraction pattern is used to form the passive structure, for example directly based on resin. The passive structure, resulting from a diffraction pattern, typically has a curved outline, without angle or discontinuity. For example, it has a narrow annular shape. For a positive photosensitive resin, the passive structure typically protrudes from the substrate. For example, it is in the form of a circular enclosure based on photosensitive resin, surrounding an empty space. For a negative photosensitive resin, the passive structure typically corresponds to a hollow imprint in the photosensitive layer.For example, it is presented in the form of a circular trench surrounding a promontory made of photosensitive resin. For reasons of clarity and conciseness, the examples described and illustrated below relate to a passive structure protruding from the substrate. The use of reverse resin polarity to form hollow structures is naturally conceivable.

[0010] According to one example, the substrate comprises or carries an electronic or optoelectronic device. According to one possibility, the passive structure is arranged, in projection in a direction perpendicular to the substrate, around an active part of the electronic or optoelectronic device.

[0011] The passive structure resulting from the diffraction pattern is by nature very well defined. This passive structure thus makes it possible to precisely delimit a location of the active part of the electronic or optoelectronic device. Such a delimitation makes it possible to envisage bringing the devices closer to each other. The pitch separating two optoelectronic devices, such as two adjacent LEDs, can typically be reduced. The passive structures surrounding each of these LEDs, advantageously formed by means of well-resolved diffraction patterns, are very distinct from each other. They also make it possible to individualize each LED effectively. The integration density of LEDs on a screen can thus be increased.

[0012] Implementation of the method typically requires standard lithography equipment and one or more standard photolithography resins. The passive structure is thus inexpensive to manufacture. Such a method can therefore advantageously be used to improve the resolution of LED-based systems with limited cost.

[0013] Another aspect relates to a passive structure on a substrate, the passive structure being formed by the method according to the invention. Another aspect relates to an optoelectronic device comprising an active part configured to emit or receive light radiation, and a passive structure projecting from the substrate, the passive structure being formed by the method according to the invention, the passive structure being arranged around the active part, in projection in a direction perpendicular to the layers of the stack.

[0014] Another aspect relates to a system comprising a plurality of optoelectronic devices arranged on or in a substrate, each optoelectronic device comprising an active part configured to emit or receive light radiation, and a plurality of passive structures projecting from the substrate, the passive structures being formed by the method according to the invention, so that each optoelectronic device is surrounded by a passive structure, in projection in a direction perpendicular to the substrate.

[0015] The advantages described above for the method can be applied mutatis mutandis to the device or system. BRIEF DESCRIPTION OF THE FIGURES

[0016] The aims, objects, as well as the characteristics and advantages of the invention will emerge more clearly from the detailed description of embodiments thereof which are illustrated by the following accompanying drawings in which:

[0017] [Fig. 1A][Fig. 1B] Figures 1A, 1B schematically illustrate different mask patterns according to embodiments of the present invention.

[0018] [Fig.lC][Fig.lD] Figures IC, 1D schematically illustrate the diffraction phenomena associated with the different mask patterns illustrated in Figures 1A, 1B according to embodiments of the present invention.

[0019] [Fig.2] [Fig.2] illustrates different diffraction patterns obtained by simulation for different mask pattern dimensions and for different defocus distances, according to embodiments of the present invention.

[0020] [Fig.3] [Fig.3] is a scanning electron microscopy image showing passive structures obtained according to one embodiment of the present invention.

[0021] [Fig.4A][Fig.4B] Figures 4A and 4B schematically illustrate two variants of optoelectronic devices comprising a passive structure according to embodiments of the present invention.

[0022] [Fig.5A][Fig.5B][Fig.5C] Figures 5A, 5B and 5C schematically illustrate variants of optoelectronic devices comprising a passive structure and a reflector according to embodiments of the present invention.

[0023] [Fig.6A][Fig.6B] Figures 6A and 6B schematically illustrate an optoelectronic device and its production method, respectively in top view and in sectional view, according to an embodiment of the present invention.

[0024] [Fig.7A][Fig.7B] Figures 7A and 7B schematically illustrate an optoelectronic device and its production method, respectively in top view and in sectional view, according to another embodiment of the present invention.

[0025] The drawings are given as examples and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily on the scale of practical applications. In particular, the dimensions of the various constituent elements of the passive structures and the optoelectronic devices are not necessarily representative of reality. DETAILED DESCRIPTION

[0026] Before beginning a detailed review of embodiments of the invention, it is recalled that the invention may in particular comprise the following optional characteristics which may be used in association or alternatively:

[0027] According to one example, the method is a method of manufacturing a passive structure for an optoelectronic device, the method comprising: • A formation of a photosensitive layer based on a photosensitive resin on a stack of layers comprising at least in part the op device electronics, • An exposure of the photosensitive layer through a lithography mask comprising at least one mask pattern, the exposure being configured to form in the photosensitive layer a diffraction pattern generated by the mask pattern, • A formation, from the diffraction pattern, of the passive structure projecting from the stack of layers, so that the passive structure is arranged, in projection in a direction perpendicular to the layers of the stack, around an active part of the optoelectronic device configured to emit or receive light radiation.

[0028] According to one example, the diffraction pattern comprises a first insolated portion at right angles to the mask pattern, a non-insolated portion substantially at right angles to the edges of the mask pattern and at right angles to the mask pattern up to the first insolated portion, and a second insolated portion extending at right angles to a region of the mask free of mask pattern on the other side of the first insolated portion relative to the non-insolated region.

[0029] According to one example, the step of forming said passive structure comprises a revealing step making it possible to form a wall projecting from the photosensitive layer at the location of the non-exposed portion. It is the production of the wall from a non-exposed portion substantially under the edge of the mask pattern and between an exposed external zone and exposure by radiation diffracted under the mask pattern which makes it possible to produce small walls. The production of such a wall, which results from a very thin non-exposed portion between two exposed portions, is not obtained directly by a very small mask pattern. A very small mask pattern cannot be used with devices of limited precision (in particular due to diffraction).Rather than avoiding diffraction phenomena as is usually the case in photolithography, the method according to the invention takes advantage of these diffraction phenomena to overcome the size limitations of the usable masks.

[0030] According to one example, the mask pattern comprises a disc or a ring or a strip. Other shapes are also conceivable.

[0031] According to one example, the disk has a diameter d less than or equal to 20 pm, the ring has a width 1 less than or equal to 20 pm, or the band has a width less than or equal to 20 pm.

[0032] According to one example, the mask pattern comprises a disk with a diameter d less than or equal to 20 pm or a ring with a width 1 less than or equal to 20 pm. According to one example, the diameter d of the disk is between 2 pm and 20 pm. According to one example, the width 1 of the ring is between 2 pm and 20 pm. It is not necessary to use mask patterns having submicron dimensions. This allows the use of standard photolithography equipment. Generally, the mask pattern can have different shapes respecting the sizing rules recommended to benefit from the principle of the present invention. Typically, the shape of the mask pattern can be solid and / or continuous, occulting and small. The concept of small size is advantageous when it is desired that the first portions exposed from at least two opposite edges, in the case of the strip or ring, or from all the edges in the case of the disc, meet. The concept of small size is advantageous for the formation of a single hollow surrounded by two very thin walls corresponding substantially to each of the edges.

[0033] According to one example, the lithography mask is moved away from the photosensitive layer by a so-called defocusing distance of between 5 pm and 200 pm, for example between 10 pm and 200 pm. This makes it possible to modulate the magnification of the diffraction pattern projected onto the photosensitive layer. It is thus possible to adjust the shape and / or the dimensions of the diffraction pattern. According to one example, the light source is moved away from the lithography mask so as to obtain the diffraction pattern by defocusing.

[0034] According to one example, the insolation of the photosensitive layer is carried out by insolation light radiation with a wavelength between 200 nm and 450 nm, for example for a wavelength of 248 nm (deep UV) or for a wavelength of 365 nm (near UV).

[0035] According to one example, the diffraction pattern is an Airy spot comprising a central disk and at least one concentric ring surrounding the central disk. The central disk is illuminated and surrounded by a first dark ring. The first dark ring is itself surrounded by a first (illuminated) light ring. The first light ring is itself surrounded by a second dark ring, etc. These rings typically correspond to diffraction fringes. The illumination intensity varies radially away from the center of the central disk. The light central disk and the first light ring, when exposed to a positive photosensitive resin, give hollow patterns after developer. The passive structure thus obtained is similar to a resin ring corresponding to the first dark ring.If the second dark ring and the second light ring are sufficiently contrasted, the passive structure can appear as two concentric rings of resin corresponding respectively to the first dark ring and the second dark ring.

[0036] According to one example, the photosensitive resin is of the positive type.

[0037] According to one example, the method further comprises depositing metal on a wall of the passive structure. The passive structure is thus typically in the form of a metallized ring. It can serve as a reflector for the light radiation emitted or received by the optoelectronic device.

[0038] According to one example, the substrate comprises or carries an optoelectronic device. According to one example, the passive structure has at least one closed contour surrounding the optoelectronic device and defining a cavity. According to one example, the method further comprises filling the cavity with at least one color converter (CCM).

[0039] According to one example, the at least one color converter comprises quantum dots (QDs). The quantum dots typically convert or filter a wavelength of light radiation emitted or received by the optoelectronic device. The wavelength of the light re-emitted by the quantum dots depends on the size and composition of these quantum dots. According to another example, the at least one color converter is in the form of an organic material. According to another example, the at least one color converter comprises phosphors.

[0040] According to one example, the passive structure comprises at least a first concentric ring and a second concentric ring. According to one example, the method further comprises localized deposition of metallic ink between the first and second rings. This forms a metallic ring between the first and second rings of the passive structure. This metallic ring can typically act as a reflector for the optoelectronic device.

[0041] According to one example, the method further comprises depositing a resin loaded with diffusing particles around the passive structure. This resin loaded, typically with diffusing particles, for example based on SiO2, TiO2, Al2O3, may be opaque or reflective. This makes it possible to localize the emission or reception of light through the passive structure.

[0042] According to one example, the method further comprises, prior to the formation of the photosensitive layer, a formation or a transfer of a plurality of optoelectronic devices on the substrate. According to one example, the passive structures are formed so that each optoelectronic device is surrounded by a passive structure, in projection in a direction perpendicular to the substrate.

[0043] According to one example, the passive structure or each passive structure is configured to contain and / or support at least one material intended to interact with the light radiation. This material may have optical properties of diffusion, conversion or reflection for example.

[0044] According to one example, the passive structure or each passive structure has at least one closed contour defining a cavity around the active part of the corresponding optoelectronic device, preferably centered on the active part, in projection in the direction perpendicular to the substrate.

[0045] According to one example, the cavity comprises at least one color converter intended to change a wavelength of light radiation.

[0046] According to one example, the passive structure or each passive structure comprises a metallized wall so as to form a reflector for the light radiation. This metallized wall may be located on different parts of the passive structure. It may be located on an outer periphery of the passive structure, or on an inner periphery, or even be internal to the passive structure.

[0047] According to an example, the passive structure or each passive structure comprises a first concentric ring and a second concentric ring, the first ring having a diameter smaller than the second ring and defining a first cavity preferably centered on the active part of the corresponding optoelectronic device, in projection in the direction perpendicular to the substrate, the second ring defining a second cavity around the first cavity, the second cavity being located between the first and second rings. The second cavity is typically in the form of a channel surrounding the first ring, and surrounded by the second ring.

[0048] According to one example, the first cavity comprises at least one color converter for modifying or converting the wavelength of the light radiation. According to one example, the second cavity comprises a metallic material forming a reflector for the light radiation and / or for the converted light radiation.

[0049] According to one example, the optoelectronic devices are light-emitting diodes and the substrate carries the light-emitting diodes and comprises an electrical connector configured to electrically power and / or control the light-emitting diodes. The light-emitting diodes (LEDs) can thus be fixed and / or connected to the substrate before producing the passive structures by photolithography. The passive structures are advantageously formed after transferring the LEDs onto the substrate. Such a substrate can be called a “backplane”. The lithography technologies for handling this type of substrate are typically less precise than the lithography technologies for manufacturing the LEDs. The substrate is typically a backplane comprising tracks and on which thousands of LEDs are deposited. A backplane-type substrate is not a silicon-based wafer-type substrate.

[0050] According to one example, the electrical connection between the substrate and the LEDs is made directly from below the LEDs, on tracks of the substrate or via connection pads between the substrate and the LEDs, or by means of microwires connecting the LEDs and the substrate. This connection can be made before the process for producing the passive structure(s). Advantageously, after formation of the passive structures, the remaining end-of-process steps relate to the deposition of the color converters (CCM).

[0051] According to one example, the passive structure has lateral dimensions comprised between 2 pm and 8 pm.

[0052] Unless incompatibility exists, technical features described in detail for a given embodiment may be combined with technical features described in the context of other embodiments described by way of example and not limitation, so as to form another embodiment which is not necessarily illustrated or described. Such an embodiment is obviously not excluded from the invention.

[0053] The term "optoelectronic device" means a device capable of emitting, conveying, or receiving light. According to a particular application, such an optoelectronic device comprises light-emitting diodes (LEDs), in particular LEDs forming the sub-pixels of an emissive screen pixel.

[0054] The invention can be implemented more broadly for different optoelectronic devices. The invention can for example be implemented in the context of laser or photovoltaic devices.

[0055] The LEDs or optoelectronic devices typically have, in the context of the present invention, dimensions, in projection in a base plane xy, less than 100 pm X 100 pm, preferably less than 10 pm X 10 pm.

[0056] Unless explicitly stated, it is specified that, in the context of the present invention, the relative arrangement of a second layer interposed between a first layer and a third layer does not necessarily mean that the layers are in direct contact with each other, but means that the second layer is either directly in contact with the first and third layers, or separated from them by at least one other layer or at least one other element.

[0057] Thus, the terms and phrases “take support”, “overcome”, “cover” or “cover over” do not necessarily mean “in contact with”.

[0058] The steps of the method as claimed are understood in the broad sense and may optionally be carried out in several sub-steps. Several embodiments of the invention implementing successive steps of the manufacturing method are described below. Unless explicitly stated, the adjective "successive" does not necessarily imply, even if this is generally preferred, that the steps follow one another immediately, intermediate steps being able to separate them.

[0059] Furthermore, the term "step" does not necessarily mean that the actions carried out during a step are simultaneous or immediately successive. Certain actions of a first step may in particular be followed by actions linked to a different step, and other actions of the first step may be repeated subsequently. Thus, the term step does not necessarily mean unitary and inseparable actions in time and in the sequence of phases of the process.

[0060] In this patent application, the terms "light-emitting diode", "LED" or simply "diode" are used synonymously. An "LED" may also be understood as a “micro-LED” or a “smart LED”. A “smart LED” is an LED associated with its own control electronics, for example based on CMOS transistors, allowing the LED to be controlled from data received, for example from a connection to a backplane.

[0061] In the present patent application, the electronic device may simply be the LED, or may comprise the LED and the passive structure associated therewith.

[0062] A substrate, a layer, a device, “based” on a material M, is understood to mean a substrate, a layer, a device comprising this material M only or this material M and possibly other materials, for example alloying elements, impurities or doping elements. Thus, a GaN-based diode typically comprises GaN and AlGaN or InGaN alloys.

[0063] In the context of the present invention, a resin is conventionally defined as an organic or organo-mineral material which can be shaped by exposure to a beam of electrons, photons or X-rays or mechanically.

[0064] Examples of resins conventionally used in microelectronics include resins based on polystyrene (PS), methacrylate (for example Polymethyl methacrylate PMMA), Hydrosilsesquioxane (HSQ), polyhydroxystyrene (PHS), etc. The advantage of using a resin is that it is easy to deposit a significant thickness, from several hundred nanometers to several microns.

[0065] Anti-reflective layers and / or coatings may be associated with the resins. This makes it possible in particular to improve the lithography resolution. In the following, the various resin-based masks are preferably associated with such anti-reflective layers.

[0066] In the context of the present invention, a “transparent” object or material means that the object or material allows at least 90% of the light intensity of the light beam passing through it to pass through. Conversely, a material or surface is considered “opaque” when it absorbs or stops at least 85% of the intensity of an incident light beam.

[0067] A reference frame, preferably orthonormal, comprising the axes x, y, z is shown in certain appended figures. This reference frame is applicable by extension to the other figures in the same sheet of figures.

[0068] In the present patent application, we will preferably speak of thickness for a layer and of height for a structure or a device. The thickness is taken along a direction normal to the main extension plane of the layer, and the height is taken perpendicular to the base plane xy. Thus, a layer typically has a thickness along z, when it extends mainly along an xy plane, and a projecting element, for example a color conversion module, has a height along z. The relative terms "on", "under", "underlying" refer preferentially at positions taken along the z direction. In the present application, “vertical”, “vertically” mean “directed along the z direction” and “lateral”, “laterally” mean “directed along a direction of the xy plane”.

[0069] An element located "perpendicular to" or "in line with" another element means that these two elements are both located on the same line perpendicular to a plane in which a lower or upper face of a substrate or a layer mainly extends, that is to say on the same line oriented vertically in the cross-sectional figures.

[0070] Dimensional values ​​are understood to be within manufacturing and measurement tolerances.

[0071] The terms “substantially”, “approximately”, “of the order of” mean, when they relate to a value, “within 10%” of this value or, when they relate to an angular orientation, “within 10°” of this orientation. Thus, a direction substantially normal to a plane means a direction having an angle of 90+10° relative to the plane.

[0072] In the following, different embodiments of the invention are detailed with regard to the corresponding figures. One principle of the invention is to generate a diffraction pattern during photolithography to form well-resolved, low-cost passive structures at the end of the optoelectronic device integration process. According to this principle, the passive structures obtained by diffraction typically have dimensions or at least some dimensions smaller than the dimensions of the mask pattern that enabled them to be generated. This principle can thus be advantageously applied to standard photolithography equipment, which is used in particular after transferring the LEDs onto a backplane, or a screen or a display panel, to form small, well-resolved passive structures.

[0073] Photolithography typically uses a mask through which light radiation is transmitted to expose an underlying photosensitive resin layer. Such a mask comprises a transparent matrix, for example quartz, and opaque mask patterns, for example chrome-based.

[0074] Figures 1A and 1B respectively illustrate a first mask pattern 11 and a second mask pattern 12 that can be used to implement the method according to the invention. The first mask pattern 11 is typically in the form of a disk, for example based on chromium, with a diameter d of between 2 μm and 20 μm, for example of the order of 5 μm. The second mask pattern 12 is typically in the form of a ring, for example based on chromium, with a width 1 of between 2 μm and 20 μm, for example of the order of 5 μm. These first and second mask patterns 11, 12 typically make it possible to generate diffraction figures or patterns of the Airy spot type when they are illuminated by radiation. near UV with a wavelength between 350 nm and 450 nm. In order for the diffraction patterns to be formed and projected onto the photosensitive layer after passing through the lithography mask, the lithography mask is moved away from the photosensitive layer by a so-called defocusing distance df typically between 10 pm and 200 pm.

[0075] Figures 1C and 1D illustrate a step of exposing a photosensitive resin layer C20 on a substrate S through a mask distant from the photosensitive resin layer by a defocusing distance df, the mask comprising respectively the first mask pattern 11 ([Fig. 1C]) and the second mask pattern 12 (Figures 1D). The exposure radiation R is deflected by diffraction on the edges of the mask patterns 11, 12 to be distributed according to a PI profile of interference fringes in the layer C20. For a mask pattern having a symmetry of revolution such as a disk or a ring, the PI profile of interference fringes also has a symmetry of revolution. The diffraction phenomenon is used here to expose certain parts of the C20 layer located directly under the mask pattern 11, 12. This makes it possible to reduce the dimension(s) in the xy plane of the passive structure obtained after exposure.It is thus possible to obtain passive structures of different shape and size from those of the mask pattern, advantageously smaller and / or better resolved than the mask pattern. The structures obtained following exposure and revelation are also illustrated in Figures 1C and 1D. The first mask pattern 11 makes it possible to form the annular passive structure 20. The second mask pattern 12 makes it possible to form the passive structure 21 comprising two concentric rings 21a, 21b.

[0076] [Fig. 2] illustrates diffraction patterns obtained by simulation for different diameters of a disk-shaped mask pattern 11 and for different defocusing distances. The simulations were carried out here for an insolation light radiation of wavelength 365 nm and for an insolation power of 0.1 W / m2. In [Fig. 2], the first row of diffraction patterns corresponds to a mask pattern diameter of 5 pm. The second row of diffraction patterns corresponds to a mask pattern diameter of 10 pm. The first column of diffraction patterns corresponds to a defocusing distance of 150 pm. The second column of diffraction patterns corresponds to a defocusing distance of 200 pm.

[0077] By moving the lithography mask away from the photosensitive layer, the diffraction patterns have a clear central spot C (Airy spot) inside the projected mask pattern M, then a succession of more or less contrasted dark and light concentric rings, outside the projected mask pattern M, which correspond to diffraction fringes. The size and / or shape of the mask pattern M is not directly reproduced on the photosensitive layer: the mask pattern M generates a diffraction pattern that is projected onto the photosensitive layer. The size and / or shape of the diffraction pattern differs from the shape of the mask pattern M.

[0078] In the following, these particular diffraction patterns are used to form a passive structure in a photosensitive resin. When the photosensitive resin is positive, the exposed resin areas become soluble in the developer. The light areas of the diffraction pattern thus correspond to areas of resin removal, and the dark areas of the diffraction pattern correspond to areas where the resin is retained. The use of a mask pattern 11 as illustrated in [Fig.lA] typically makes it possible to form a passive structure in the form of a circular enclosure surrounding a cavity. The use of a mask pattern 12 as illustrated in [Fig.lB] typically makes it possible to form a passive structure in the form of a double concentric circular enclosure.

[0079] The passive structures can be formed directly in a suitable resin, for example in a resin having a refractive index of the order of 1.1 to 1.2. The passive structures can be formed indirectly from a standard resin, by transferring the patterns from the standard resin to another resin with low reflectivity or to an oxide layer. Those skilled in the art know how to transfer patterns formed in standard resins to other layers, for example by etching.

[0080] [Fig.3] illustrates passive structures 20 based on positive photosensitive resin, obtained here after exposure of a resin layer through a lithography mask comprising mask patterns 11 in the form of a 5 pm diameter disc, for a defocusing distance between the mask and the resin layer of 5 pm. The lithography equipment used here is a standard MA8 mask aligner from Süss Microtec operating with a 365 nm UV lamp. The passive structures 20 obtained result from the diffraction patterns illustrated in [Fig.2]. The passive structures 20 here retain a single resin ring after exposure. The passive structures 20 are here in the form of a crucible with a closed contour of the order of 5 pm in diameter and approximately 2 pm in height.The final shapes and dimensions of passive structures obtained by photolithography via diffraction patterns depend in particular on the size of the mask patterns, the defocusing distance, the exposure dose and the exposure wavelength, the type of resist and the thickness of the resist. It is thus possible to obtain taller and / or wider passive structures for example, depending on the requirements. It is also possible to obtain passive structures comprising two or more concentric rings. A mask pattern in the form of a ring typically generates a passive structure comprising two concentric rings. A mask pattern comprising two concentric rings typically generates a passive structure comprising four concentric rings. The passive structures are intended to be integrated into . optoelectronic devices comprising an active part configured to emit or receive light radiation.

[0081] Figures 4A and 4B illustrate two examples of passive structures 20 obtained from mask patterns 11 in the form of discs as illustrated in [Fig.lA]. These passive structures 20 are here formed around an active part of the optoelectronic device, typically a light-emitting diode LED 31, 32. The dimensions of the passive structures 20 are adapted according to the dimensions of the LEDs. As illustrated in [Fig.4A], the passive structure 20 may have a diameter d20 of approximately 6 pm and a height h20 of approximately 5 pm for an LED 31 2 pm wide along x and 1 pm high along z. The pitch of an array of LEDs 31 surrounded by such passive structures 20 may here be advantageously reduced between 10 pm and 20 pm. As illustrated in [Fig.4B], the passive structure 20 may have a diameter d20 of approximately 8 pm and a height h20 of approximately 8 pm for an LED 32 in the form of a wire 1 pm wide along x and 5 pm high along z.This makes it possible to have a clearance distance d23 between the wire 32 and the passive structure 20 of approximately 3 pm, at mid-height h 20 / 2. The pitch of an array of LEDs 32 surrounded by such passive structures 20 can here be of the order of 40 pm.

[0082] The passive structures may advantageously be functionalized to improve or optimize the operation of the optoelectronic devices. The passive structures may, for example, contain and / or support one or more materials configured to absorb, modify, or reflect the X-wavelength light radiation emitted or received by the optoelectronic device.

[0083] Figures 5A, 5B, 5C illustrate different embodiments of a diffuser or a reflector associated with a passive structure according to the invention. In particular, [Fig.5A] illustrates an embodiment in which a layer 40 of resin loaded with diffusing particles (WPR for "white photoresist"), typically particles based on TiO2, is formed on the external periphery 201 of the passive structure 20. The internal space 200 delimited by the passive structure 20 is devoid of a layer 40 of loaded resin. The internal space 200 forms a clearance for the LED 31. The layer 40 of loaded resin typically makes it possible to diffuse and / or reflect a portion of the light radiation emitted by the LED 31. A layer 40 of the WPR type typically has a reflectivity of the order of 80% to 95%. This allows the light emitted by the LED 31 to be reflected. Optical losses and / or parasitic coupling (“cross talk”) are reduced.The light extraction and / or the directivity of the LED are improved. [Fig.5B] illustrates an embodiment in which a metallic layer 50, for example based on aluminum, is deposited on the external periphery 201 of the passive structure 20. This metallic layer 50 typically makes it possible to reflect part of the light radiation emitted by the LED 31. The light extraction and / or the . directivity of the LED are improved. [Fig.5C] illustrates an embodiment in which the passive structure 21 is obtained from a mask pattern 12 in the form of a ring as illustrated in [Fig.1B]. The passive structure 21 here comprises two concentric rings 21a, 21b. The channel located between these two rings 21a, 21b is here filled with a layer 60 of resin loaded with silver particles. This layer 60 typically forms a reflector for the LED 31. The light extraction and / or the directivity of the LED are improved.

[0084] It is understood that the devices comprising the functionalized passive structures 20, 21 illustrated in FIGS. 5A, 5B, 5C may perfectly comprise an active part of the LED type 32 in the form of a wire as illustrated in [Fig.4B], or other active parts of the laser or photovoltaic cell type for example. The shapes and dimensions of the passive structures 20, 21, and the type of functionalization of these passive structures, may in particular depend on the type of active part housed in the space 200 of the optoelectronic device.

[0085] Figures 6A, 6B illustrate another embodiment of an optoelectronic device comprising an LED 31 and passive structure 20, in which the passive structure 20 supports on its external periphery 201 a layer 40 of resin loaded with diffusing particles, and in which the internal space of the passive structure 20 is filled by a layer 70 of resin loaded with color converters (CCM). The color converters can typically be in the form of quantum dots (QD), phosphors or organic material. As illustrated in [Fig.6B], the internal space of the passive structure 20 can be filled 700 in a localized manner by inkjet. The formulation of the ink is chosen so as to confer the desired optical properties for the layer 70. The passive structure 20 is thus doubly functionalized.It allows both a diffusion / reflection function to be provided on its external periphery, via layer 40, and a wavelength conversion or wavelength filter function via the color converters of layer 70.

[0086] Figures 7A, 7B illustrate another embodiment of an optoelectronic device comprising an LED 31 and a passive structure 21, in which the channel of the passive structure 21 is here filled by a layer 60 of resin loaded with silver particles, and in which the internal space of the passive structure 21 is here filled by a layer 70 of resin loaded with color converters. As illustrated in [Fig.7B], the filling 600 of the channel located between the rings 21a, 21b of the passive structure 21 can be carried out in a localized manner by inkjet. The internal space of the passive structure 21 can be filled in a localized manner by inkjet, as previously. The different fillings 600, 700 are typically carried out at the end of the process. This makes it possible to avoid cross-contamination between different equipment used. in microelectronics technologies. The formulation of the inks is chosen so as to confer the desired optical properties for the layers 60, 70. The passive structure 21 is thus doubly functionalized. It allows both a reflection function to be provided via the layer 60, and a wavelength conversion or wavelength filter function via the QDs of the layer 70.

[0087] It is clear from the preceding examples of embodiment that the method according to the invention makes it possible to form a well-defined passive structure, at low cost, and advantageously functionalizable.

[0088] The formation of these passive structures is advantageously compatible with the manufacturing steps at the end of the process at the screen or display panel level after LED transfer, or at the integration level on a PCB type substrate. The formation of the passive structures can advantageously be done directly on a backplane. At this stage, the use of materials to form reflectors on the passive structures, for example of the silver type, is not problematic with respect to the manufacturing equipment, unlike the LED formation steps involving manufacturing equipment sensitive to metal contamination.

[0089] The invention is not limited to the embodiments previously described. Other diffraction patterns may be implemented, for example for other applications of the passive structures. The passive structures may contain or support materials having varied properties, depending on the needs and applications. Those skilled in the art will be able to adapt the principle of the invention to different applications without difficulty.

Claims

Claims

1. Method for manufacturing a passive structure (20, 21) on a substrate, the method comprising: • A formation of a photosensitive layer based on a photosensitive resin on said substrate, • An exposure of said photosensitive layer through a lithography mask comprising at least one mask pattern (11, 12), said exposure being configured to form in said photosensitive layer a diffraction pattern) generated by said mask pattern (11, 12), • A formation, from said diffraction pattern, of said passive structure (20, 21) in said photosensitive layer on said substrate.

2. The method of claim 1, wherein the diffraction pattern comprises a first insolated portion at right angles to the mask pattern, a non-insolated portion substantially at right angles to the edges of the mask pattern and at right angles to the mask pattern up to the first insolated portion, and a second insolated portion extending at right angles to a region of the mask free of mask pattern on the other side of the first insolated portion relative to the non-insolated region.

3. A method according to claim 2, wherein the step of forming said passive structure (20, 21) comprises a revealing step for forming a wall projecting from the photosensitive layer at the location of the non-exposed portion.

4. A method according to the preceding claim, wherein said mask pattern (11, 12) comprises a disc, a ring or a strip.

5. Method according to the preceding claim, in which the disc has a diameter d less than or equal to 20 pm, the ring has a width 1 less than or equal to 20 pm, or the strip has a width less than or equal to 20 pm.

6. Method according to any one of the preceding claims, in which said lithography mask is spaced from said photosensitive layer by a so-called defocusing distance of between 5 pm and 200 pm.

7. A method according to any preceding claim, wherein said diffraction pattern (C, Al) is an Airy spot. comprising a central disc (C) and at least one concentric ring (Al) surrounding said central disc (C).

8. A method according to any preceding claim, wherein said photosensitive resin is of the positive type.

9. A method according to any preceding claim further comprising depositing metal on a wall of said passive structure (20, 21).

10. A method according to any one of the preceding claims wherein said substrate comprises or carries an optoelectronic device, and wherein said passive structure (20, 21) has at least one closed contour surrounding said optoelectronic device and defining a cavity (200), said method further comprising filling (700) said cavity (200) with at least one color converter.

11. A method according to any preceding claim wherein said passive structure (21) comprises at least a first concentric ring (21a) and a second concentric ring (21b).

12. A method according to the preceding claim further comprising a localized deposition (600) of metallic ink between said first and second rings (21a, 21b).

13. Method according to any one of the preceding claims further comprising a deposition of resin loaded with diffusing particles, typically TiO2-based particles, around said passive structure (20, 21).

14. A method according to any one of the preceding claims further comprising, prior to the formation of said photosensitive layer, a formation or transfer of a plurality of optoelectronic devices on said substrate, and in which said passive structures (20, 21) are formed so that each optoelectronic device is surrounded by a passive structure (20, 21), in projection in a direction perpendicular to said substrate.

15. A system comprising a plurality of optoelectronic devices arranged on or in a substrate, each optoelectronic device comprising an active portion (31, 32) configured to emit or receive light radiation, and a plurality of passive structures (20, 21) projecting from the substrate, the passive structures (20, 21) being formed by the method according to any one of the preceding claims so that each optoelectronic device is surrounded by a passive structure (20, 21), in projection according to a direction perpendicular to said substrate.

16. System according to the preceding claim, in which each passive structure (20, 21) is configured to contain and / or support at least one material intended to interact with the light radiation.

17. System according to any one of claims 15 to 16, in which each passive structure (20, 21) has at least one closed contour defining a cavity (200) centered on the active part (31, 32) of said corresponding optoelectronic device, in projection in the direction perpendicular to said substrate.

18. System according to the preceding claim, wherein said cavity (200) comprises at least one color converter intended to modify a wavelength of the light radiation.

19. System according to any one of claims 15 to 18, wherein each passive structure (20, 21) comprises a metallized wall so as to form a reflector for said light radiation.

20. System according to any one of claims 15 to 19, wherein each passive structure (21) comprises a first ring (21a) and a second ring (21b) concentric, said first ring (21a) having a diameter smaller than the second ring (21b) and defining a first cavity (200) centered on said active part (31, 32) of said corresponding optoelectronic device, in projection in the direction perpendicular to said substrate, said second ring (21b) defining a second cavity around said first cavity (200) and located between said first and second rings (21a, 21b).

21. System according to the preceding claim, wherein said first cavity (200) comprises at least one color converter intended to modify a wavelength of the light radiation, and wherein said second cavity comprises a metallic material (60) forming a reflector for the light radiation.

22. A system according to any one of claims 15 to 21, wherein said optoelectronic devices are light-emitting diodes and wherein said substrate carries said light-emitting diodes and comprises electrical connections configured to electrically power and / or control said light-emitting diodes.

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