Method for manufacturing a three-dimensional structure in bending

Abstract

Title: Method for Manufacturing a Three-Dimensional Bending Structure. The invention relates to a method for manufacturing a three-dimensional structure comprising supplying a stack (1) consisting of, stacked along a so-called vertical direction (Z), a support substrate (400), a sacrificial layer (300), a layer of interest (200) having a flank (203), and a tensor layer (100) having a flank (103), the tensor layer having a residual stress σ100. The method also includes removing a shrinkage portion (350) of the sacrificial layer, while retaining a remaining portion (360) of the sacrificial layer underlying the layer of interest. The shrinkage portion is located at the edge of a lateral portion (250) of the layer of interest extending from the entire flank of the layer of interest.The residual stress σ100 of the tensor layer is configured to cause bending of the layer of interest during the shrinkage step of the shrinkage portion. Figure for the abstract: Fig.2M.

Description

Title of the invention: Method for manufacturing a three-dimensional flexural structure technical field

[0001] The present invention relates to the field of three-dimensional (3D) microstructures, more precisely to microstructures exhibiting controlled deformation. Its application is particularly advantageous in the field of microlenses. PRIOR TECHNOLOGY

[0002] Several techniques exist for manufacturing 3D microstructures with controlled deformation, particularly for the fabrication of microlenses. Microlenses are generally produced by optical lithography followed by thermal finishing, as developed by Popovic, ZD, Sprague, RA, and Connell, GAN, in the publication "Technique for monolithic fabrication of microlens arrays," Applied Optics, 27(7):1281 (1988). These techniques can present difficulties in terms of reproducibility and predictability of the shape obtained after finishing. Other techniques exist for obtaining microlens arrays, notably grayscale lithography, which is increasingly being studied for the fabrication of 3D structures. Grayscale lithography often involves numerous lithography steps, resulting in high costs. Another commonly used method is 3D pattern printing.This technique uses a structured mold of micro-bols obtained by optical lithography and / or etching. These patterns are then imprinted in a resin, thus forming microlenses. Creating the mold can be challenging when the desired dimensions are small.

[0003] In a field unrelated to the fabrication of microlenses, it has been observed that microdisks used in photonics as two-dimensional whispering-gallery resonators can deform upon release from the substrate due to stress relaxation, taking on a chip-like shape (see, in particular, Li Y. et al., Three-Dimensional Ani-sotropic Microlaser from GaN-Based Self-Bent-Up Microdisk, ACS Photonics 2018, 5, 11, 4259-4264, 2018, one of whose figures is reproduced in [Fig. 1]). However, the shape of the microdisk after deformation depends entirely on its own stresses and cannot be controlled.

[0004] An objective of the present invention is therefore to propose a method for deforming microstructures, particularly microlenses, allowing the final shape of the structure to be controlled in a reproducible manner and by inducing a limited budget.

[0005] Furthermore, the method of deforming a microdisk under the effect of stress relaxation following its release from the substrate, as described in the prior art, only allows its deformation in a single direction of bending, this direction of bending being induced by the stresses existing within the microdisk. Another objective of the invention is to provide a common solution for both tensile and compressive deformation. SUMMARY

[0006] To achieve this objective, according to one embodiment, a manufacturing process for a three-dimensional structure is provided, comprising the following steps: a. supplying a stack comprising at least, stacked in a so-called vertical direction: i. a supporting substrate, ii. a sacrificial layer, iii. a layer of interest delimited in all directions by a plane perpendicular to the vertical direction, called the horizontal plane, by a limb, iv. a tensor layer bounded in all directions of the horizontal plane by a flank, the tensor layer exhibiting a residual stress Oioo, b. a withdrawal of a portion of the sacrificial layer, called the withdrawal portion, selectively from the layer of interest and the tensor layer, the withdrawal portion forming a closed contour in projection in the horizontal plane, the withdrawal portion being entirely located at the right of a lateral portion of the layer of interest extending from the entire flank of the layer of interest, the withdrawal of the withdrawal portion being carried out so as to retain a portion of the sacrificial layer, called the remaining portion, located at the right of the layer of interest and the sacrificial layer.

[0007] The residual stress GiOo of the tensor layer is configured to cause a bending of the layer of interest during the withdrawal step of the withdrawal portion.

[0008] In this process, the removal of the shrinkage portion of the sacrificial layer allows for the partial mechanical release of the layer of interest and the tensor layer. The presence of the tensor layer and its mechanical properties make it possible to constrain the layer of interest into a given shape during release. The characteristics of the tensor layer, and in particular its residual stress, can be parameterized so as to force the layer of interest into a desired shape. It is therefore possible, through the use of the tensor layer, to very precisely control the shape of the structure obtained at the end of the process.

[0009] As will be shown later, both the direction and the magnitude of the deformation of the layer of interest induced by the process according to the invention can be precisely defined and predicted by numerical simulations, which makes it easier to control the deformation.

[0010] Thus, the invention makes it possible to obtain three-dimensional structures, particularly microlenses, with good control of the final shape, in a reproducible manner and while inducing a limited budget.

[0011] Another aspect of the invention relates to a method for manufacturing a three-dimensional structure exhibiting rotational symmetry along the vertical direction. The method comprises the following steps: a. a supply of a stack comprising, stacked in a so-called vertical direction: i. a supporting substrate, ii. a sacrificial layer, iii. a layer of interest delimited in all directions by a plane perpendicular to the vertical direction, called the horizontal plane, by a limb exhibiting rotational symmetry about the vertical direction, iv. a tensor layer bounded in all directions of the horizontal plane by a flank exhibiting rotational symmetry along the vertical direction, the tensor layer exhibiting a residual stress Oioo, b. a withdrawal of a portion of the sacrificial layer, called the withdrawal portion, selectively from the layer of interest and the tensor layer, the withdrawal portion forming a closed contour in projection in the horizontal plane, the withdrawal portion being located opposite a lateral portion of the layer of interest extending from the entire flank of the layer of interest, the withdrawal of the withdrawal portion being carried out so as to retain a portion of the sacrificial layer, called the remaining portion, located opposite the layer of interest and the sacrificial layer.

[0012] The residual stress GiOo of the tensor layer is configured to cause a bending of the layer of interest during the withdrawal step of the withdrawal portion. BRIEF DESCRIPTION OF THE FIGURES

[0013] The aims, objects, features and advantages of the invention will become clearer from the detailed description of an embodiment thereof, which is illustrated by the following accompanying drawings in which:

[0014] [Fig. 1] Fig. 1, extracted from the prior art, illustrates a layer that has undergone a de- training following a relaxation of its constraints.

[0015] [Fig. 2A] Figures 2A to 2M represent a first embodiment of the method according to the invention. [Fig. 2A] illustrates the provision of an initial stack comprising a support substrate, a sacrificial layer and a layer of interest.

[0016] [Fig.2B] Fig.2B illustrates the deposition of a tensor layer on the layer of interest.

[0017] [Fig.2C] [Fig.2C] illustrates the deposition of a masking layer on the layer tensor.

[0018] [Fig.2D] The [Fig.2D] illustrates the structuring of the masking layer according to a chosen pattern.

[0019] [Fig.2E] Fig.2E illustrates the transfer of the pattern to the tensor layer through the masking layer.

[0020] [Fig.2F] [Fig.2F] illustrates the transfer of the pattern to the layer of interest through the masking layer.

[0021] [Fig.2G] The [Fig.2G] illustrates the removal of the masking layer.

[0022] [Fig. 2H] Figures 2H to 2J illustrate the progressive withdrawal of a portion of the withdrawal of the sacrificial layer while leaving a remaining portion in place.

[0023] [Fig.2I]

[0024] [Fig.2J]

[0025] [Fig.2K] Fig.2K illustrates the bending of the layer of interest and the tensor layer following their release through the withdrawal step.

[0026] [Fig.2L] The [Fig.2L] illustrates the withdrawal of the tensor layer.

[0027] [Fig.2M] Fig.2M illustrates a substrate underlying a plurality of 3D structures formed by the process according to the invention.

[0028] [Fig.2N] The [Fig.2N] is a view from below of the remaining portion and of the layer of interest in the case where the latter have a circular shape.

[0029] [Fig.20] [Fig.20] is a bottom view of the remaining portion and layer of interest in the case where the latter have an elliptical shape.

[0030] [Fig.2P] The [Fig.2P] is a cross-sectional view of the stack before and after deformation.

[0031] [Fig. 3A] Figures 3A to 30 represent a second embodiment of the method according to the invention. [Fig. 3A] illustrates the provision of an initial stack comprising a support substrate, a sacrificial layer, and a layer of interest.

[0032] [Fig.3B] Fig.3B illustrates the nanostructuring of the layer of interest.

[0033] [Fig. 3C] [Fig. 3C] illustrates the deposition of a planarization layer on the layer of interest.

[0034] [Fig.3D] The [Fig.3D] illustrates the deposition of a tensor layer on the planarization layer.

[0035] [Fig. 3E] [Fig. 3E] illustrates the deposition of a masking layer on the layer tensor.

[0036] [Fig.3F] The [Fig.3F] illustrates the structuring of the masking layer according to a chosen pattern.

[0037] [Fig.3G] Fig.3G illustrates the transfer of the pattern to the tensor layer through the masking layer.

[0038] [Fig.3H] Fig.3H illustrates the transfer of the pattern to the planarization layer and to the layer of interest through the masking layer.

[0039] [Fig.31] Fig.31 illustrates the removal of the masking layer.

[0040] [Fig.3J] Figures 3J to 3L illustrate the progressive removal of a portion of the sacrificial layer while leaving a remaining portion in place.

[0041] [Fig.3K]

[0042] [Fig.3L]

[0043] [Fig.3M] Fig.3M illustrates the bending of the layer of interest and the tensor layer following their release through the withdrawal step.

[0044] [Fig.3N] The [Fig.3N] illustrates the withdrawal of the tensor layer.

[0045] [Fig.30] The [Fig.30] illustrates the removal of the planarization layer.

[0046] [Fig. 4A] Figures 4A to 4L represent a third embodiment of the method according to the invention. [Fig. 4A] illustrates the provision of an initial stack comprising a support substrate, a sacrificial layer, and a layer of interest.

[0047] [Fig.4B] Fig.4B illustrates the deposition of a tensor layer on the layer of interest.

[0048] [Fig.4C] [Fig.4C] illustrates the deposition of a layer of secondary interest on the layer tensor.

[0049] [Fig.4D] Fig.4D illustrates the nanostructuring of the secondary layer of interest.

[0050] [Fig.4E] Fig.4E illustrates the deposition of a masking layer on the secondary layer of interest.

[0051] [Fig. 4F] [Fig. 4F] illustrates the structuring of the masking layer according to a pattern selected.

[0052] [Fig.4G] The [Fig.4G] illustrates the transfer of the pattern to the secondary layer of interest, to the tensor layer and to the layer of interest through the masking layer.

[0053] [Fig.4H] ​​Fig.4H illustrates the removal of the masking layer.

[0054] [Fig. 41] Figures 41 to 4K illustrate the progressive withdrawal of a portion of the withdrawal of the sacrificial layer while leaving a remaining portion in place.

[0055] [Fig.4J]

[0056] [Fig.4K]

[0057] [Fig.4L] [Fig.4L] illustrates the bending of the layer of interest, the tensor layer and of the secondary layer of interest following their release through the withdrawal step.

[0058] [Fig.5] Fig.5 represents the profile of the layer of interest after removal of the sacrificial layer for different diameters of the plot.

[0059] [Fig.6A] Fig.6A represents the profile of the layer of interest as the shrinkage portion of the sacrificial layer is withdrawn, for a layer of interest and a tensor layer having a diameter of 15 pm.

[0060] [Fig.6B] [Fig.6B] is a scanning electron microscopy (SEM) image of the same assembly as in [Fig.6A], after complete removal of the shrinkage portion of the sacrificial layer.

[0061] [Fig.7A] Fig.7A represents the profile of the layer of interest as the shrinkage portion of the sacrificial layer is withdrawn, for a layer of interest and a tensor layer having a diameter of 20 pm.

[0062] [Fig.7B] Figures 7B to 7D are scanning electron microscopy (SEM) images of the same assembly as in [Fig.7A], after complete removal of the shrinkage portion of the sacrificial layer.

[0063] [Fig.7C]

[0064] [Fig.7D]

[0065] [Fig.8A] Figure [Fig.8A] illustrates the experimental (solid lines) and theoretical results (dotted lines) of the profile of the layer of interest obtained for different diameters of residual plots.

[0066] [Fig.8B] The [Fig.8B] illustrates the maximum deflection obtained as a function of the diameter of the residual plot by numerical simulations (square points) and experimentally (triangular points).

[0067] The drawings are given by way of example and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate understanding of the invention and are not necessarily to scale with practical applications. In particular, the dimensions are not representative of reality. DETAILED DESCRIPTION

[0068] Before proceeding with a detailed review of embodiments of the invention, optional features that may be used in combination or alternatively are listed below:

[0069] According to one example, the removal of the withdrawal portion is carried out so as to expose the lateral portion of the layer of interest.

[0070] According to an advantageous embodiment, the flank of the layer of interest and the flank of the tensor layer each have a substantially elliptical or substantially circular shape in projection into the horizontal plane.

[0071] According to an advantageous embodiment, the remaining portion has a flank having a substantially elliptical or substantially circular shape in projection into the horizontal plane.

[0072] According to a preferred example, the flank of the layer of interest, the flank of the layer The tensor and the flank of the remaining portion each have a substantially circular shape when projected onto the horizontal plane. The layer of interest has a diameter D200 in the horizontal plane, and the remaining portion has a diameter D360 in the horizontal plane. After the removal of the removal portion, the layer of interest has a slant height f200, with f200 > 0.05 * (D200 - D360), preferably f200 > 0.10 * (D200 - D360).

[0073] According to an advantageous example, the layer of interest has a diameter D200 in the horizontal plane, and the remaining portion has a diameter D360 in the horizontal plane. After the removal of the removal portion, the ratio D200 / D360 is greater than 2, preferably greater than 3.

[0074] According to a preferred example, the flank of the layer of interest, the flank of the tensor layer, and the flank of the remaining portion each have a substantially elliptical shape when projected onto the horizontal plane. The layer of interest has a minor axis D2ooy in the horizontal plane, and the remaining portion has a minor axis D360y in the horizontal plane. After the removal of the removal portion, the layer of interest, in cross-section along a plane perpendicular to the horizontal plane and containing the minor axis of the layer of interest, has a slant height f200, with f2ooy > 0.05 * (D2ooy - D360y), preferably f2ooy > 0.05 * (D2ooy - D360y), y - D360y.

[0075] Preferably, at least during the withdrawal step, the flank of the tensor layer is in the extension of the flank of the layer of interest in the vertical direction.

[0076] Advantageously, the process further comprises, after the step of removing the shrink portion, a step of removing the tensor layer.

[0077] According to one example, the bending of the layer of interest brings its flank closer to the substrate.

[0078] Advantageously, the process is configured so that the bending of the layer of interest causes the layer of interest to come into contact with the supporting substrate.

[0079] Preferably, the process includes bonding at least part of the layer of interest with the supporting substrate.

[0080] Preferably, the bonding of at least part of the layer of interest with the supporting substrate is caused at least in part, and preferably solely, by bringing the layer of interest into contact with the supporting substrate.

[0081] According to one example, the bending of the layer of interest moves its flank away from the substrate.

[0082] According to an example, the layer of interest has a thickness e200 along the direction vertical with e200 < 300 nm. This limits the residual stress required in the tensor layer to allow deformation of the layer of interest. It also reduces the stiffness of the layer of interest.

[0083] According to an example, which | Oioo | >500 MPa and preferably | Oioo | >1000 MPa. This ensures significant deformation of the layer of interest

[0084] According to a preferred example, before the shrinkage step, the layer of interest has a residual stress o20o with | o20o | <100 MPa. This makes it possible to limit the stress residual energy is required in the tensor layer to allow deformation of the layer of interest. This makes it possible to achieve deformations of the layer of interest of several nanometers or even micrometers.

[0085] According to one example, the sacrificial layer is based on at least one of an oxide such as SiO2 or SiON, or a nitride such as SiN. The sacrificial layer may also be a silicon-based anti-reflective coating (designated in English by the acronym SiARC, "Silicon containing Anti-Reflective Coating"). The sacrificial layer is advantageously removable by etching with HF or H3PO4. In the case of a sacrificial layer based on a nitride such as SiN, in order to facilitate removal with HF, the nitride in question may advantageously be deposited at a low temperature, for example at a temperature below 500°C, or be oxygenated.

[0086] According to one example, the tensor layer is based on at least one of TiN, AlN, SiN and Si3N4. Advantageously, the tensor layer is based on a metal.

[0087] According to one example, the layer of interest is based on at least one of Si and SiGe. Advantageously, the layer of interest is based on a conductive material.

[0088] According to one example, the layer of interest is based on an amorphous material. This makes it possible to overcome variations in intrinsic physical properties related to crystal directions. This therefore makes it possible to homogenize the deformation.

[0089] According to a preferred embodiment, the layer of interest, after the step of removing the shrinkage portion of the sacrificial layer, forms a lens.

[0090] According to a preferred embodiment, the stack comprises a plurality of distinct layers of interest contained in the same plane parallel to the horizontal plane before the step of removing the portion of the sacrificial layer.

[0091] According to one example, the stacking comprises a plurality of distinct layers of interest above a single substrate.

[0092] Preferably, each layer of interest forms a lens.

[0093] According to one embodiment, the process includes, prior to the step of removing the portion of the sacrificial layer, a step of structuring at least one layer of interest.

[0094] Preferably, the structuring step of at least one layer of interest is carried out before the stack provisioning step.

[0095] According to one embodiment, the stacking further comprises a secondary interest layer above the tensor layer, the withdrawal of the withdrawal portion is also done selectively at the secondary interest layer, and the process further comprises, prior to the withdrawal portion step, a structuring step of the secondary interest layer.

[0096] According to one example, the structuring stage includes the implementation of at least a technique among optical lithography, block copolymer self-assembly and nanoprinting.

[0097] The residual stresses present in certain materials, as referred to in this application, are induced by the various stages of deposition and processing of these materials. Residual stresses in a layer can be of mechanical origin, particularly generated during its formation. They are then often linked to the deposition methods and conditions. Residual stresses can also be of thermal origin. They then depend on the thermal variations experienced by the layer, its thermal properties, and those of the substrate on which it rests. This thermal component can therefore change during the manufacturing stages.

[0098] Various methods can be used to measure the residual stress in a layer. X-ray diffraction (XRD) is typically used. By adapting the wavelength of the emitted X-rays according to the material being studied and by studying the angular distribution of the X-rays diffracted by the sample, a curve can be plotted relating the interplanar spacing d to the measured angle and the material properties (typically a curve of the type d = sin2(π)). The curve thus obtained makes it possible to determine the state and level of stress of the sample in the measured direction. The residual stress can also be measured by laser interferometry. In this case, the radius of curvature of the substrate supporting the layer whose residual stress level is to be determined is measured before and after the layer is deposited (or before and after a layer processing step).Mechanical stress values ​​are calculated directly using Stoney's formula, given the thickness of the layer and substrate, their respective Young's moduli, and Poisson's ratios. Furthermore, the residual stress level can be measured by Raman spectroscopy, a technique based on variations in the Raman frequencies of optical phonons. This technique offers the advantages of being non-destructive, highly sensitive, and providing sub-nanometer spatial resolution.

[0099] It is specified that, within the framework of the present invention, the terms "on", "overcomes", "covers", "underlying", "opposite" and their equivalents do not necessarily mean "in contact with". Thus, for example, the depositing, transferring, gluing, assembling or applying a first layer on a second layer does not necessarily mean that the two layers are directly in contact with each other, but means that the first layer at least partially covers the second layer by being either directly in contact with it or by being separated from it by at least one other layer or at least one other element.

[0100] A layer may also be composed of several sub-layers of the same material or of different materials.

[0101] A substrate, layer, or device "based on" a material M is understood to mean a substrate, layer, or device comprising only that material M or that material M and possibly other materials, for example, alloying elements, impurities, or dopant elements. Thus, a material based on a III-N material may comprise a III-N material with added dopants.

[0102] The term "selective etching with respect to" or "etching exhibiting selectivity with respect to" means an etching configured to remove a material A or a layer A with respect to a material B or a layer B, and having an etching speed of material A greater than the etching speed of material B. The selectivity is the ratio of the etching speed of material A to the etching speed of material B. The selectivity between A and B is denoted SA:B.

[0103] A coordinate system, preferably orthonormal, comprising the X, Y, Z axes is shown in figures 2A, 3A and 4A. This coordinate system is applicable by extension to the other figures.

[0104] In this patent application, the terms thickness for a layer and height for a structure or device will preferably be used. Height is measured perpendicular to the horizontal XY plane. Thickness is measured in a direction normal to the principal plane of extension of the layer. Thus, a layer typically has a thickness along Z when it extends mainly along the horizontal XY plane, and a projecting element, for example an insulation trench, has a height along Z. The relative terms "on," "under," and "below" preferably refer to positions measured along the Z direction.

[0105] The terms "approximately", "about", "in the order of" mean "within 10%, preferably within 5%".

[0106] A first embodiment of a three-dimensional structure will be described with reference to Figures 2A to 2M. For clarity, steps 2A to 2L illustrate the obtaining of a single three-dimensional structure. Naturally, these steps allow for the simultaneous obtaining of numerous three-dimensional structures from the same substrate, as illustrated in the final Figure 2M.

[0107] Figures 2A to 2G illustrate a sequence of steps to obtain a stacking 1, illustrated in [Fig.2G], which will be the subject of the process according to the invention.

[0108] Figure 2A illustrates the provision of an initial stack comprising a support substrate 400, a sacrificial layer 300 and a layer of interest 200. Preferably, the layer of interest 200 is in contact with the sacrificial layer 300. However, it is conceivable that another layer may be intercalated along the vertical Z direction between the sacrificial layer 300 and the layer of interest 200.

[0109] A tensor layer 100 is then deposited on, preferably directly on, the layer of interest 100, as illustrated in [Fig. 2B]. The tensor layer 100 is typically deposited at low temperature, for example at a temperature below 250°C for a TiN deposition on a SoC (“System On Chip”).

[0110] Figures 2C to 2H illustrate a first structuring of the stack obtained in [Fig. 2B], for example by lithography. This first structuring can be described as microstructuring. A masking layer 50 is first deposited on the tensor layer 100, and then it is itself structured, for example by photolithography, as illustrated in [Fig. 2D]. The masking layer 50 is typically a photosensitive resin. Next, the tensor layer 100 ([Fig. 2E]) and then the layer of interest 200 ([Fig. 2F]) and possibly the sacrificial layer 300 are etched through the masking layer 50. These etching steps are preferably carried out by an anisotropic etching method such as reactive ion etching or plasma etching. The masking layer 50 is then removed, for example by stripping ([Fig.2G]).

[0111] This gives us the stack 1 illustrated in [Fig.2G] which is provided during the first step of the process according to the invention.

[0112] This stacking 1 is described in more detail below.

[0113] The stacking 1 comprises, stacked along the vertical direction Z, the support substrate 400, the sacrificial layer 300, the layer of interest 200 and the tensor layer 100. The layer of interest 200 and the tensor layer 100 each have a flank 203, 103 delimiting them in the horizontal XY plane.

[0114] Preferably, the tensor layer 100 completely covers the layer of interest 200. Advantageously, the layer of interest 200 and the tensor layer 100 have the same shape when projected onto the horizontal XY plane. Preferably, the layer of interest 200 and the tensor layer 100 overlap when projected onto the horizontal XY plane. In other words, the flank 103 of the tensor layer is preferably an extension of the flank 203 of the layer of interest 200 along the vertical Z direction.

[0115] According to a preferred embodiment, the flank 203 of the layer of interest 200 has a substantially circular shape when projected onto the horizontal XY plane ([Fig. 2N]). In other words, when projected onto the horizontal plane, the layer of interest 200 has the shape of a disk. The circular shape is particularly well-suited for the fabrication of lenses or even microlenses from the layer of interest 200. It is understood, however, that these layers can take any shape when projected onto the horizontal XY plane, depending on the intended applications.

[0116] Similarly, according to a preferred embodiment, the flank 103 of the tensor layer 100 has a substantially circular shape when projected onto the horizontal XY plane. In other words, when projected onto the horizontal plane, the tensor layer 100 has the shape of a disk.

[0117] When the flank 203 of the layer of interest 200 presents, in projection in the plane horizontal XY, a substantially circular shape, a diameter of the layer of interest 200 is defined, denoted D200. Similarly, when the flank 103 of the tensor layer 210 presents, in projection onto the horizontal XY plane, a substantially circular shape, a diameter of the tensor layer 100 is defined, denoted DiOo-

[0118] The structuring of the layer of interest 200 to define its flank 203 is preferably referred to as microstructuring. Typically, D200 < 1000 pm (10⁶ meters) and preferably D200 < 100 pm, preferably D200 < 10 pm and preferably D200 < 5 pm. Furthermore, preferably D200 > 20 nanometers.

[0119] The layer of interest 200 and the tensor layer 100 can also exhibit, when projected onto the horizontal XY plane, a substantially elliptical shape ([Fig. 20]). In this case, a minor axis D2Oo,y and a major axis D2OojX are defined for the layer of interest 200, and a minor axis DiOo,y and a major axis DiOo,x for the tensor layer 100. The minor and major axes can also be designated as minor and major diameters.

[0120] A second step of the process according to the invention, illustrated in Figures 2H to 2J, consists of a partial withdrawal of the sacrificial layer 300 selectively from the layer of interest 200 and the tensor layer 100. More precisely, in this step, a withdrawal portion 350 is removed from the sacrificial layer 300 while leaving in place a remaining portion 360 of this same layer 300. Figures 2H to 2J illustrate the progressive withdrawal of the withdrawal portion 250. The stack obtained after the complete withdrawal of the withdrawal portion 250 is illustrated in [Fig. 2J].

[0121] The withdrawal portion 350 and the remaining portion 360 are described in more detail below.

[0122] The recession portion 350 extends entirely along a lateral portion 250 of the layer of interest 200 in the vertical direction Z. The lateral portion 250 of the layer of interest 200 extends from the entire flank 203 of the layer of interest. Thus, in projection onto the horizontal XY plane, when both the flank 203 of the layer of interest 200 and the flank 363 of the remaining portion 363 are circular, and when the remaining portion 360 of the sacrificial layer is centered with respect to the layer of interest 200, the lateral portion 250 has the shape of a circular ring. This example is illustrated in Figures 2H to 2J.

[0123] The recessed portion 350 also defines, at its inner flank 354, a closed contour projected onto the horizontal XY plane. This closed contour corresponds in particular to the projection onto the horizontal XY plane of the flank 363 of the remaining portion 360. Indeed, the inner flank 354 of the recessed portion 350 and the flank 363 of the remaining portion 360 coincide. Advantageously, this closed contour is circular. When this is the case, a diameter of the remaining portion 360, denoted D360, is defined.

[0124] The remaining portion 360 of the sacrificial layer 300 is located opposite a so-called central portion 260 of the layer of interest 200.

[0125] A lateral portion 150 and a central portion 160 of the tensor layer 100 are also defined, located respectively at the right of the lateral portion 250 of the layer of interest 200 and at the right of the central portion 260 of the layer of interest 200.

[0126] The remaining portion 360 of the sacrificial layer forms a plot 360 in this example.

[0127] According to an advantageous embodiment of the invention, the layer of interest 200, the tensor layer 100, and the plot 360 all have a circular shape when projected onto the horizontal XY plane and are concentric in this same plane. The assembly consisting of the plot 360, the layer of interest 200, and the tensor layer then exhibits rotational symmetry about an axis 1000 parallel to the vertical Z direction.

[0128] The removal of the withdrawal portion 350 and its effects on the stacking 1 will now be described.

[0129] The removal of the withdrawal portion 350 is carried out by etching, typically by vapor phase hydrofluoric acid (HF) etching.

[0130] This withdrawal allows a partial mechanical release of the layer of interest 200 and the tensor layer 100. This release is particularly effective at the lateral portion 250 of the layer of interest 200 and the lateral portion 150 of the tensor layer 100. Indeed, during the stacking supply step 1, and generally before the withdrawal step, the layer of interest 200 and the tensor layer 100 rest entirely on the sacrificial layer 300 and are therefore held by it. Once the withdrawal portion 350 is removed, the layer of interest 200 and the tensor layer 100 are left suspended on the pad 360. They rest on the pad 360 at the central portion 260 of the layer of interest 200 and, indirectly, at the central portion 360 of the tensor layer 100. The pad 360 is thus the only element connecting the support substrate 400 and the layer of interest 200.

[0131] The tensor layer 100 and the layer of interest 200 each exhibit, before the mechanical release step, a residual stress denoted respectively O100 and o200. These residual stresses O100 and o200 are generated by the deposition conditions of the layers they characterize. They can be either tensile or compressive. In the particular case of a SOI (Silicon On Insulator) substrate, whose upper silicon layer can act as the layer of interest, the fabrication of the substrate generally generates a tensile residual stress in the silicon, typically from a few MPa to a few GPa.

[0132] Due to the removal of the shrinkage portion 350, the residual stresses O100 and o200 cause deformations of the layer of interest 200 and the tensor layer 100, particularly at their lateral portions 250 and 150. In this sense, [Fig. 2J] illustrates a theoretical step in which the shrinkage portion 350 would be removed and the The layers of interest 200 and tensor 100 would appear to have the same shape as before this removal. Such a stacking is actually unstable: the deformation of the layer of interest 200 and the tensor 100 layer occurs immediately after the removal and even during the removal process. Figure 2K illustrates the stacking exhibiting this deformation.

[0133] The residual stress o2oo of the layer of interest 200 is generally determined by the various steps it undergoes upstream of the process according to the invention. Thus, it is the residual stress Oioo of the tensor layer 100 that is configured to allow the desired deformation of the layer of interest 200. The sign of the sum of the residual stress Oioo of the tensor layer 100 and the residual stress o2oo of the layer of interest indicates the direction of the deformation of the layer of interest 200 caused by the tensor layer 100 (movement of the layer of interest 200 towards or away from the supporting substrate 400). The amplitude of the deformation of the layer of interest 200 is also determined by the configuration of the residual stress Oioo of the tensor layer 100.

[0134] The residual stress Oioo of the tensor layer 100 is chosen according to the desired bending by taking into account various parameters and in particular the residual stress o20o of the layer of interest 200 and the thickness e2Oo along the vertical direction Z of the layer of interest 200.

[0135] The thickness e in the vertical Z direction of the tensor layer 100 is also a parameter that directly impacts the residual stress Oi00. The greater the thickness e100, the lower the residual stress O100. When the tensor layer 100 is TiN-based, the thickness e100 is typically between a few nanometers, for example 2 nanometers, and about 100 nanometers. The thickness e100 is generally chosen according to the materials used in order to obtain the desired stress level in the tensor layer 100.

[0136] The various parameters, including in particular the thickness e100 of the tensor layer 100 and its residual stress o100, can be chosen to induce tension or compression of the layer of interest 200, and thus cause it to move away from or towards the substrate support 400. The process according to the invention can therefore deform the layer of interest 200 in both directions of the vertical Z direction. Titanium nitride (TiN) and silicon nitride (SiN), and nitrides more generally, have the advantage of being able to be in tension or compression depending on their deposition conditions. They are therefore very interesting materials for the fabrication of the tensor layer 100. TiN, in particular, is compressive over ranges from a few hundred MPa to a few GPa and for a thickness of a few nanometers to a hundred nanometers.

[0137] By using specific deposition conditions and correctly dimensioning the different layers, it is therefore possible to induce the desired deformation (direction and amplitude) of the layer of interest 200. A person skilled in the art is perfectly capable of adapting these parameters to obtain the desired deformation.

[0138] It should be noted that the residual stresses On”, (Loo) can be adjusted, at least locally, to mitigate or exacerbate the bending caused by the shrinkage step. This can be achieved by carrying out thermal annealing or ion implantation in these layers before the shrinkage step. Thermal annealing can optionally take place during the shrinkage step, and ion implantation can also be carried out after the shrinkage step.

[0139] Thermal annealing induces a relaxation of the mechanical stresses in the layer. The residual stress will depend primarily on the difference in coefficient of thermal expansion between the substrate and the annealed layer, or between the annealed layer and the underlying layer. It is therefore possible, for example, by relaxing the mechanical stresses before or during the process according to the invention, to reduce a layer initially under compressive stress to one under tensile stress.

[0140] Ion implantation can make it possible to modify the stresses on certain localized areas of the layer of interest 200 and / or the tensor layer 100. This allows very precise control of the curvature during the withdrawal step.

[0141] Thus, the partial removal step of the sacrificial layer 300, or release step, allows a bending of the layer of interest 200, this bending being able to be perfectly controlled, even locally.

[0142] Figure 2P is a cross-sectional view of the stack showing both the layer of interest 200 and the tensor layer 100 before (dashed lines) and after (solid lines) deformation. This figure shows how the deformation of the layer of interest 200 can be quantified.

[0143] In the advantageous case where the layer of interest 200 and the plot 360 both have a circular shape in projection onto the horizontal XY plane and are concentric in this same plane, as is the case in [Fig. 2P], the deformation can be measured along the vertical Z direction, between: a. an upper plane 1001 in which is included the lower face 252 of the central portion 250 of the layer of interest 200, and b. a lower plane 1002, parallel to the upper plane 1001 and passing through the lower edge 204 of the layer of interest 200, generally constituting the area of ​​the layer of interest 200 that has undergone the greatest vertical displacement. The lower edge 204 of the layer of interest 200 is defined by the intersection of the flank 203 of the layer of interest 200 and its lower face 202.

[0144] The distance along the vertical direction Z between these two planes 1001, 1002 is named arrow of the layer of interest 200 and is denoted f2oo.

[0145] When the layer of interest 200 and the plot 360 are in contact as illustrated In [Fig.2P], the upper face 361 of the plot 360 is also included in the upper plane 1001.

[0146] The lower face 202 of the layer of interest 200 is also typically included in the upper plane 1001 before deformation.

[0147] In general, even when the stacking does not admit rotational symmetry, the deformation of the layer of interest 200 can be characterized at any point on the edge 204 of the layer of interest 200 by a local deflection. The deflection f2Oo of the layer of interest 200 will typically be considered equivalent to the deformation measured at the point on the edge 204 exhibiting the highest local deflection.

[0148] In the case where the layer of interest 200 is deformed so as to be brought closer to the support substrate 400, at least partial contact between the layer of interest 200 and the support substrate 400 can be sought at the level of the upper face 401 of the latter. Advantageously, the various parameters of the process are configured so that this contact induces at least partial bonding of the layer of interest 200 and the support substrate 400. According to a particular embodiment, the contact alone ensures the bonding. Such bonding is notably possible when the support substrate 400 and the layer of interest 200 are based on the same material, for example silicon. When the layer of interest 200 is deformed until it is bonded to the support substrate 400, the height hientiiie of the resulting structure, typically a lens, is equal to the sum of the height h360 of the plot 360 and the thickness e2oode of the layer of interest 200 (see figures 2J and 2L).Since the thickness e200 of the layer of interest 200 is generally small relative to the height h360 of the plot 360, in this case we make the approximation h lens ~ h360*.

[0149] As illustrated by the transition from [Fig.2K] to [Fig.2L], the tensor layer 100 is advantageously removed after the partial removal step of the sacrificial layer 300. This allows the layer of interest 200 to be exposed. In the case of a Si layer of interest and a TiN tensor layer, a wet etching called SCI (NH4OH / H2O2 / H2O cleaning bath, with a ratio generally ranging from 1:2:2 to 1:1:5) allows a total and selective removal of the TiN with respect to the Si.

[0150] This removal is facilitated when at least partial bonding of the layer of interest 200 to the upper face 401 of the support substrate 400 has taken place. Indeed, thanks to the bonding, the layer of interest 200 remains in place and retains the shape imparted to it by the tensor layer 100. When it is not bonded to the support substrate 400, the layer of interest 200 risks undergoing further deformation during the removal of the tensor layer 100. This new deformation would be oriented in the opposite direction to the deformation occurring during the partial removal step of the sacrificial layer 300. This embodiment thus further improves control over the final shape imparted to the three-dimensional structure. Bonding the layer of interest to the support substrate 400 can prevent this second deformation. It is understood, however, that in the event of a lack of bonding between the layer of interest 200 and the supporting substrate 400, this second deformation can also be anticipated and taken into account to obtain the desired final deformation.

[0151] Although Figures 2A to 2L illustrate the implementation of the process for a single three-dimensional structure, it is understood that the process according to the invention can be implemented for a plurality of three-dimensional structures sharing the same substrate support 400. Figure 2M illustrates the result that would then be obtained. Reference numerals 200a, 200b, and 200c designate the different layers of interest of each of the structures obtained, visible from this view. The steps described with reference to Figures 2A to 2L can be carried out simultaneously for a plurality or even all of the structures. In this embodiment, before removing the portion of the shrinkage associated with each layer of interest 200a, 200b, and 200c, these layers have a face arranged in the same plane, here a horizontal plane. Typically, the upper faces of the layers of interest 200a, 200b, 200c can form distinct disks arranged in the same plane.

[0152] The following paragraphs aim to propose several combinations of materials that can be used for each of the layers of the stack 1. Naturally, these examples are not limiting and the process described can be implemented with many other materials.

[0153] Example 1: a. Substrate support: Si or glass b. Sacrificial layer: SiO2 c. Layer of interest: Si or SiGe d. Tensor layer: TiN or NiT

[0154] Example 2: a. Substrate support: Si or glass b. Sacrificial layer: SiARC c. Layer of interest: Si or SiGe d. Tensor layer: TiN or AIN

[0155] Example 3: a. Substrate support: Si or glass b. Sacrificial layer: SiON c. Layer of interest: Si or SiGe d. Tensor layer: TiN or AIN

[0156] Example 4: a. Substrate support: Si or glass b. Sacrificial layer: SiN c. Layer of interest: Si, for example amorphous silicon d. Tensor layer: TiN or AIN

[0157] Example 5: a. Substrate support: Si or glass b. Sacrificial layer: SiN c. Layer of interest: SiGe d. Tension layer: TiN or AIN

[0158] The process according to the invention can be the subject of numerical simulations carried out using the finite element method (commonly referred to by the English acronym FEM, "Finite Element Method"). The purpose of these simulations is to predict the various dimensional and experimental parameters necessary to obtain a structure with the desired shape and dimensions. Typically, the aim is to determine the lateral dimensions of the pad 360 – and therefore the etching time of the sacrificial layer 300 – required to obtain the desired bend, for example, a bend leading to the bonding of the layer of interest 200 to the support substrate 400.

[0159] The simulations whose results are presented in [Fig. 5] concern the specific and preferred case of circular structures. We are therefore particularly interested in the diameters of the layers of interest and tensor 100, 200, and the diameter of the pad 360. The objective here is to determine the etching time required for the diameter of the pad 360 to be such that the bending of the layer of interest 200 leads to its bonding to the support substrate 400, as a function of the height of the pad 360. The other parameters (materials, thicknesses of the layer of interest 200 and the tensor layer 100, etc.) are fixed. It should be noted that in this non-limiting example, the objective being to obtain bonding of the layer of interest 200 to the support substrate 400, the height h360 of the pad 360 corresponds to the height hientine of the lens obtained at the end of the process.

[0160] The structure incremented in the software comprises an SOI substrate including a buried oxide (BOX) acting as a sacrificial layer and a silicon layer acting as the layer of interest. The buried oxide, based on SiO2, has a thickness of 2 pm in the vertical Z direction, while the silicon layer has a thickness of 50 nm. A titanium nitride (TiN) layer acts as a tensor layer and has a thickness of 30 nm.

[0161] When projected onto the horizontal XY plane, the layer of interest and the tensor layer have a diameter of 15 pm. These layers rest on a SiO2 pad with a height of 2 pm and a diameter varying from 1 to 10 pm. The ratio between the height and the diameter of the lens obtained at the end of the process is therefore equal to 7.5.

[0162] The different curves of the graph shown in [Fig. 5] correspond to the same simulation, carried out for different values ​​of diameter D360 of the SiO2 360 block (curve 51: D360=1pm, curve 52: D360=2pm, curve 53: D360=3pm, curve 54: D360 (=4pm, curve 55: D360=5pm, curve 56: D360=6pm, curve 57: D360=7pm, curve 58: D360=8pm, curve 59: D360=9pm, curve 510: D360=10pm). They thus illustrate the deflection of the layer of interest 200 (silicon layer) as a function of the diameter of the 360 ​​pad.

[0163] In particular, these results predict a homogeneous bend of 2 pm for a SiO2 pad with a diameter of 2 pm. The height h360 of the SiO2 pad is 2 pm (thickness of the BOX). Therefore, h360 = length for d360 = 2 pm. This simulation thus allows us to predict that the SiO2 pad must have a diameter of 2 pm to achieve bonding of the layer of interest 200 with the support substrate 400. The etching conditions of the sacrificial layer (SOI BOX) follow directly from this.

[0164] The process according to the invention therefore has the advantage of producing results that can be easily anticipated. Its implementation is thus facilitated, and the structures obtained perfectly correspond to the specifications set.

[0165] Experimental examples will now be presented with reference to Figures 6A to 7D.

[0166] A first example is carried out with the following stacking: a. Sacrificial layer of SiO2 with a thickness of 2 pm, b. Si layer of interest with a thickness of 20 nm and a diameter of 15 pm and a residual stress of +0.133 MPa, c. TiN tensor layer having a thickness of 30 nm, a diameter of 15 pm and a residual stress of -2.02 GPa.

[0167] The lithography mask used for microstructuring allows for the creation of 5, 10, 15, and 20 µm pads from the sacrificial layer. Once the transfer has been carried out in TiN and then in silicon by dry etching, following the process described above with reference to Figures 2C to 2G, a phase-value etch using high-frequency irradiation is performed in several stages. The theoretical etching speed used is 25 nm / min. After each etching stage, the suspended, constrained disks are measured using an atomic force microscope (AFM) ([Fig. 6A]), and then cross-sectional scanning electron microscopy (SEM) images are taken after the last etching stage ([Fig. 6B]).

[0168] A first etching step leads to an initial release characterized by a residual SiO2 pad with a diameter of 12 pm. This initial release results in a deflection of approximately 40 nanometers (curve 61). A second etching step allows for a greater release of the layer of interest and the tensor layer. It is characterized by a residual SiO2 pad with a diameter of 8 pm. It produces a deflection of approximately 440 nm (curve 62). Finally, a third and final etching step results in a residual SiO2 pad with a diameter of 5.7 pm. generates a deflection of 1000 nm (curve 63).

[0169] The cross-sectional SEM image ([Fig.6B]) confirms that at the end of the process, the 360 ​​SiO2 plot has a diameter of 5.7 pm.

[0170] A similar study was carried out with the same experimental parameters except for the diameter of the layer of interest and the tensor layer, which was fixed this time at 20 pm. The results obtained are presented in [Fig. 7A] (AFM analysis) and in Figures 7B to 7D (SEM images).

[0171] The first three etching steps give results very close to those obtained for a 15 pm disk. Indeed, the successive releases initially produce an average deflection of about 40 nanometers (curve 71), then of about 350 nm (curve 72), and finally of a maximum of 1176 nm (curve 73). The fourth and final release by etching results in residual bumps of 4.3 pm (curve 74). The AFM profile shows a deflection of about 1670 nm. However, in the SEM image reproduced in [Fig. 7B], the microdisk is in contact with the substrate, which means that deflections of 2000 nm (height of the SiO2 bump) are reached in some places. These results show that the formation of 3D structures with a height of 2 pm is achievable by controlled bending of microdisks. Furthermore, the flexed microdisks are resilient despite the thinness of the silicon (layer of interest) and titanium nitride (tensor layer) layers.

[0172] Figures 7C and 7D are SEM images taken from different viewing angles than that of [Fig. 7B], which was a cross-sectional view of the structure. These images highlight that some areas of the layer of interest exhibit greater deflection than others. Indeed, some areas of the microdisks have a greater deflection. In the case studied here, this inhomogeneous deformation can be caused by the layer of interest, which is made of silicon. In fact, the crystallinity of silicon generates different physical properties depending on the crystal directions, resulting, for example, in variations in the Young's modulus from 130 to 180 GPa. These differences in deflection may have no impact on the performance of the structure, and it is therefore possible to ignore them. If, on the other hand, one seeks to obtain homogeneous deflection, one will preferably opt for a layer of interest based on amorphous materials.The use of this type of material eliminates variations in intrinsic physical properties related to crystal directions. Deformation is therefore homogeneous throughout the entire structure.

[0173] The experimental results for the 15 pm microdisks were superimposed on the results of the simulations carried out by the finite element method.

[0174] Figure [8A] shows the experimental results in solid lines and the numerical simulations in dashed lines, for different residual block diameters (curve 81: 1 pm, curve 82: 4 pm, curves 83 and 84: 6 pm, curve 85: 7 pm, Curves 86 and 87: 8 pm, curve 88: 10 pm, curve 89: 12 pm). For residual plots of 6 and 8 pm, the deflection curves obtained by simulation perfectly overlap with the experimental ones. Thus, for a 6 pm plot, the maximum experimental deflection is 1092 nm compared to 1111 nm in the simulation.

[0175] Figure 8B represents the maximum deflection obtained as a function of the residual plot diameter for the simulation (square dot curve) and experimental (triangular dot curve) results. In addition to the close relationship between the two results, it should be noted that the maximum deflections obtained by simulation form an S-shaped curve as a function of the plot diameter. This shape agrees with the initial experimental results.

[0176] The results obtained are consistent with simulations of the fabrication of 3D microstructures by controlled bending of microstructures. This shows that the process described above makes it possible to obtain three-dimensional structures whose shapes are perfectly predictable. Furthermore, a person skilled in the art can easily establish a nomogram of 3D microstructures achievable by controlled bending.

[0177] According to an advantageous embodiment of the invention, the process includes a step of structuring the layer of interest 200 or a secondary layer of interest 200'.

[0178] This structuring can, for example, be described as nanostructuring. The patterns created by this structuring have dimensions greater than those of the layer of interest 200. Typically, nanostructuring forms patterns with critical dimensions less than one micrometer and preferably less than 500 nanometers, or even less than 100 nanometers, or even less than 20 nanometers.

[0179] Such nanostructuring can confer very advantageous properties to the structure formed. In the case of microlenses, nanostructuring can, for example, give them anti-reflective properties.

[0180] This application is inspired by the eyes of moths, whose surface can be likened to a network of microlenses, each with an anti-reflective nanometric structure. On the one hand, the microlens network focuses light onto photoreceptors, thus improving the insect's field of vision. This microlens network is obtained by bending the layer of interest according to the process described above. On the other hand, the nanometric network increases the amount of light captured by the eye by reducing light reflections, regardless of the angle of incidence. This nanometric network is obtained by texturing the layer of interest. Furthermore, the combination of these two structures—micrometric and nanometric—gives moth eyes other functionalities, such as superhydrophobicity and an anti-fog effect.

[0181] This multiple structuring is commonly called a hierarchical or multi- scale. The realization of such structures today faces strong integration constraints, the addition of a nanometric structure on a non-planar micrometric shape is not insignificant.

[0182] The process according to this embodiment constitutes a solution that first involves nanometric structuring, followed by microstructuring. Thanks to this sequence, nanostructuring is facilitated since it is carried out on a flat surface before the layer of interest is bent. This offers the advantage of flexibility with regard to the imaginable nanostructures and the nanostructuring methods that can be implemented. In particular, it is possible to use nanostructuring techniques as varied as optical lithography, self-assembly of block copolymers, or even nanoprinting. The technique used, for example the type of optical lithography, can be chosen according to the desired resolution for the nanostructuring.

[0183] A first example of the embodiment with nanostructuring is illustrated in figures 3A to 30.

[0184] Fig. 3A, like Fig. 2A, illustrates the provision of an initial stack comprising the support substrate 400, the sacrificial layer 300, and the layer of interest 200. Fig. 3B illustrates the nanostructuring of the layer of interest 200 from its upper surface 201. This nanostructuring step of the upper surface 201 allows the formation in the layer of interest 200 of nanostructures 2000 having a height hnano along the vertical Z direction and a characteristic dimension lnano in the horizontal XY plane. If the nanostructures 2000 have a square shape in projection onto the XY plane, lnano will correspond, for example, to the side of this square. Typically, lnano < 100 nanometers.

[0185] A planarization layer 500 is then deposited on the layer of interest 200 ( [Fig.3C]) in order to allow the deposition of the tensor layer ( [Fig.3D]) to take place on a flat surface.

[0186] The steps illustrated in Figures 3E to 3L are similar to the steps described previously with reference to Figures 2C to 2J. The only difference is that the etching of the stack 1 through the masking layer 50 also includes the etching of the planarization layer 500. During these steps, the layer of interest 200 is microstructured, preferably so as to give it a circular shape in the horizontal XY plane. It then has a diameter D200 in the horizontal XY plane. Typically, there is a shape ratio of between 40 and 1000 between 1 nano and D200. In one example, the patterns created by the nanostructuring are distributed over the entire surface of the layer of interest 200. Alternatively, they can be distributed over only one area of ​​the layer of interest 200 while leaving another area of ​​the layer of interest 200 free. In one example, these patterns are distributed in a way that is not specified. They can also be distributed in a non-periodic manner. This allows, for example, the nanostructure patterns to be associated with only certain angles of incidence of light rays reaching the lens coated with these nanostructures.

[0187] Following the removal of the shrinkage portion 350 of the sacrificial layer, the layer of interest and the planarization layer 50 undergo bending due to the residual stresses residing in the tensor layer 100 (transition from [Fig.3L] to [Fig.3M]).

[0188] Preferably, the tensor layer 100 ([Fig.3M]) is removed, followed by the planarization layer 500 ([Fig.3N]) in order to expose the layer of interest 200 with the previously carried out nanostructuring ([Fig.30]).

[0189] A second example of the embodiment with nanostructuring is illustrated in figures 4A to 4L.

[0190] Fig. 4A, like Fig. 2A and Fig. 3A, illustrates the provision of an initial stack comprising the support substrate 400, the sacrificial layer 300 and the layer of interest 200. As illustrated in Fig. 4B, the tensor layer 100 is then deposited on the layer of interest 200.

[0191] A secondary interest layer 200' is then deposited on the tensor layer 100 ([Fig. 4C]). This time, it is the upper surface 201' of the secondary interest layer 200' that is nanostructured ([Fig. 4D]), so as to form nanostructures s 2000'. The characteristics described in the previous example concerning the nanostructuring of the layer of interest 200 apply mutatis mutandis to the nanostructuring of the secondary interest layer 200'.

[0192] The steps illustrated in Figures 4E to 4K are similar to the steps described previously with reference to Figures 2C to 2J. The only difference is that the etching of the stack 1 through the masking layer 50 also includes the etching of the secondary layer of interest. During these steps, the secondary layer of interest 200' is microstructured, preferably so as to give it a circular shape in the horizontal XY plane. It then has a diameter D200' in the horizontal XY plane. Typically, the aspect ratio between Inano and D200' is between 40 and 1000.

[0193] Following the removal of the shrinkage portion 350 of the sacrificial layer, the layer of interest 200 and the secondary layer of interest 200' undergo bending due to the residual stresses residing in the tensor layer 100 (transition from [Fig.4K] to [Fig.4L]).

[0194] In this example, the nanostructured surface (upper surface 201' of the secondary interest layer 200') is located above the tensor layer 100 in the vertical direction. In order to be able to use this surface for various applications, the tensor layer is therefore not removed.

[0195] The nanostructured 3D structure thus obtained finds a particularly advantageous application in nanoprinting. It can indeed serve as a master mold (commonly referred to by the anglicism "master mold") in such a process.

[0196] Through the different embodiments described below, it is clear that the invention offers a high-performance and easy-to-implement solution for manufacturing 3D structures, particularly microlenses, possibly exhibiting a nanometric level of structuring.

[0197] It is understood that the principle of double structuring applied to the process according to the invention can be implemented on a larger scale. For example, a first structuring can be carried out to form an overall device (typically a lens) of several hundred micrometers using the controlled bending technique described above. A network of microlenses on the surface of the lens can be produced upstream, by a second structuring, using the same processes as those described above for obtaining a nanostructure on the surface of a microlens. In this case, the characteristic dimensions of the second structuring correspond to those of a microstructure as presented above.

[0198] The invention is not limited to the embodiments previously described and extends to all embodiments covered by the invention.

Claims

Demands

1. A method for manufacturing a three-dimensional structure comprising the following steps: • a supply of a stack (1) comprising, stacked in a so-called vertical direction (Z), at least: i. a supporting substrate (400), ii. a sacrificial layer (300), iii. a layer of interest (200) delimited in all directions by a plane perpendicular to the vertical direction (Z), called the horizontal plane (XY), by a limb (203), iv. a tensor layer (100) delimited in all directions of the horizontal plane (XY) by a flank (103), the tensor layer (100) exhibiting a residual stress Oioo, • a withdrawal of a portion of the sacrificial layer, called the withdrawal portion (350), selectively from the layer of interest (200) and the tensor layer (100), the withdrawal portion (350) forming a closed contour in projection in the horizontal plane, the withdrawal portion (350) being entirely located at the right of a lateral portion (250) of the layer of interest (200) extending from the entire flank (203) of the layer of interest (200), the withdrawal of the withdrawal portion (350) being carried out so as to retain a portion of the sacrificial layer (300), called the remaining portion (360), located at the right of the layer of interest (200) and the sacrificial layer (300), the residual stress Gioo of the tensor layer (100) being configured to cause a bending of the layer of interest (200) during the withdrawal step of the withdrawal portion (350), in which: • the flank (203) of the layer of interest (200), the flank (103) of the tensor layer (100) and the flank (363) of the remaining portion (360) each have a substantially circular shape in projection into the horizontal plane (XY), the layer of interest (200) having a diameter D2Oo in the horizontal plane (XY) and the remaining portion (360) having a diameter D360 in the horizontal plane (XY), and wherein, after the removal of the removal portion (350), the layer of interest (200) has a slant height f200, with f200 > 0.05 * (D200 - D360), preferably f200 > 0.1 (D200 - D360), or • the flank (203) of the layer of interest (200), the flank (103) of the tensor layer (100), and the flank (363) of the remaining portion (360) each have a substantially elliptical shape in projection onto the horizontal plane (XY), the layer of interest (200) having a minor axis D200,y in the horizontal plane (XY) and the remaining portion (360) having a minor axis D360 > y in the horizontal plane (XY), and wherein, after the removal of the removal portion (350), the layer of interest (200) presents, in section along a plane perpendicular to the horizontal plane (XY) and containing the small axis of the layer of interest 200, an arrow f2Oo, with f2Oo>O,O5*(D2oo,y-D36Ojy), preferably f200 >0, lO*(D2oo,y-D36ojy).

2. A method according to the preceding claim wherein the flank (203) of the layer of interest (200), the flank (103) of the tensor layer (100) and the flank (363) of the remaining portion (360) each have a substantially circular shape in projection into the horizontal (XY) plane, wherein the layer of interest (200) has a diameter D2Oo in the horizontal (XY) plane and the remaining portion (360) has a diameter D360 in the horizontal (XY) plane, and wherein, after the removal of the shrinkage portion (350), the ratio D2Oo / D36O is greater than 2, preferably greater than 3.

3. A method according to any one of the preceding claims wherein, at least during the withdrawal step, the flank (103) of the tensor layer (100) is in the extension of the flank (203) of the layer of interest (200) in the vertical direction (Z).

4. A method according to any one of the preceding claims further comprising, after the step of removing the shrink portion (350), a step of removing the tensor layer (100).

5. A method according to any one of the preceding claims configured so that bending the layer of interest (200) brings its flank (203) closer to the substrate (400).

6. Method according to the preceding claim configured so that the bending of the layer of interest (100) causes the layer of interest (200) to come into contact with the supporting substrate (400).

7. Method according to the preceding claim comprising bonding at least a part of the layer of interest (200) with the supporting substrate (400).

8. A method according to the preceding claim in which the bonding of at least part of the layer of interest (200) with the support substrate (400) is caused at least in part, and preferably solely, by bringing the layer of interest (200) into contact with the support substrate (400).

9. A method according to any one of claims 1 to 4 wherein the bending of the layer of interest (200) moves its flank (203) away from the substrate (400).

10. A method according to any one of the preceding claims wherein the layer of interest (200) has a thickness e2oo along the vertical direction (Z) with e2Oo < 300 nm.

11. A method according to any one of the preceding claims wherein Oioo > 500 MPa and preferably Oioo > 1000 MPa.

12. A method according to any one of the preceding claims wherein, before the removal step, the layer of interest (200) has a residual stress o20o with o20o <100 MPa.

13. A method according to any one of the preceding claims wherein the sacrificial layer (300) is based on at least one of an oxide such as SiO2 or SiON, and a nitride such as SiN, or is a silicon-based anti-reflective layer.

14. A method according to any one of the preceding claims wherein the tensor layer (100) is based on at least one of TiN, SiN and Si3N4.

15. A method according to any one of the preceding claims wherein the layer of interest (200) is based on an amorphous material.

16. A method according to any one of the preceding claims wherein the layer of interest (200), after the step of removing the shrinkage portion (350) of the sacrificial layer (300), forms a lens.

17. A method according to any one of the preceding claims, wherein the stack (1) comprises a plurality of distinct layers of interest (200) contained in the same plane parallel to the horizontal plane (XY) before the step of removing the portion of removal (350) of the sacrificial layer (300).

18. Method according to the preceding claim wherein each layer of interest (200) forms a lens.

19. A method according to any one of the preceding claims comprising, prior to the step of removing the removal portion (350) of the sacrificial layer (300), a step of structuring at least one layer of interest (200).

20. A method according to any one of claims 1 to 18 wherein the stack (1) further comprises a secondary interest layer (200') above the tensor layer (100), wherein the withdrawal of the withdrawal portion (350) is also done selectively at the secondary interest layer (200'), the method further comprising, prior to the withdrawal step of the withdrawal portion (350), a structuring step of the secondary interest layer (200').

21. A method according to any one of the two preceding claims wherein the structuring step comprises the implementation of at least one technique among optical lithography, self-assembly of block copolymers and nanoprinting.

Images