Optical devices and manufacturing processes for optical devices

Abstract

Optical Devices and Method for Manufacturing Optical Devices This description relates to an optical device (200) comprising: - a meta-surface (250) comprising a meta-surface substrate (251) having at least a first meta-surface layer (202) of a first material, and a pillar array (203) through the first meta-surface layer, the pillars being made of a second material different from the first material, the meta-surface having a first face (250A) and a second face (250B) opposite the first face of said meta-surface; - a first anti-reflective stack (210) having a first face (210A) and a second face (210B) opposite the first face of said first anti-reflective stack and positioned on the first face (250A) of the meta-surface; and - a metallic trace (205) having an exposed portion on the first face of the first anti-reflective stack. Figure for the summary: Fig. 3A

Description

Title of the invention: Optical devices and method of manufacturing optical devices Technical field

[0001] The present description relates generally to optical devices, and more particularly to the manufacture of optical devices. Prior art

[0002] Optical devices, such as lenses, diffusers, filters, beam shapers, mirrors, etc. are commonly used today and are increasingly used in optoelectronic devices or systems.

[0003] It would be desirable to be able to improve, at least in part, certain aspects of optical devices and the manufacture of optical devices, in particular optical devices comprising optical meta-surfaces. Summary of the invention

[0004] There is a need to improve the fabrication of optical devices, particularly optical devices comprising optical meta-surfaces.

[0005] One embodiment overcomes all or part of the drawbacks of known optical devices and known methods of manufacturing the devices.

[0006] One embodiment provides an optical device comprising: - a meta-surface comprising a meta-surface substrate having at least a first meta-surface layer of a first material, and an array of pillars across the first meta-surface layer, the pillars being made of a second material different from the first material, the meta-surface having a first face and a second face opposite the first face of said meta-surface; - a first anti-reflective stack having a first face and a second face opposite the first face of said first anti-reflective stack and positioned on the first face of the meta-surface; and - a metal trace having an exposed portion at the first face of the first anti-reflective stack.

[0007] According to one embodiment, the first meta-surface layer extends over the first face of the meta-surface.

[0008] According to one embodiment, the metal trace is included, for example incorporated, in the meta-surface substrate, the optical device comprising a first aperture extending in depth through the first anti-reflective stack and the meta-surface substrate to the exposed portion of the metal trace.

[0009] According to one embodiment, the metal trace is incorporated into a second meta-surface layer of the meta-surface substrate in contact with the first meta-surface layer, the meta-surface substrate further comprising a third meta-surface layer in contact with the second meta-surface layer and covering the metal trace, the second meta-surface layer being between the first meta-surface layer and the third meta-surface layer.

[0010] According to one embodiment, the metal trace is positioned on the first face of the first anti-reflective stack, for example corresponding to at least part of a contact pad.

[0011] According to one embodiment, the optical device further comprises a transparent substrate, for example a glass substrate, the second face of the meta-surface being located on a first face of the transparent substrate.

[0012] According to one embodiment, the optical device further comprises a second anti-reflection layer, a second face of the transparent substrate, opposite the first face of said transparent substrate, being located on said second anti-reflection layer.

[0013] One embodiment provides a method of manufacturing an optical device, the method comprising: - forming a meta-surface comprising a meta-surface substrate including at least a first meta-surface layer of a first material, and an array of pillars across the first meta-surface layer, the pillars being made of a second material different from the first material, the meta-surface having a first face and a second face opposite the first face of said meta-surface; - forming a first anti-reflective stack on the first face of the meta-surface, the first anti-reflective stack having a first face and a second face opposite the first face of said first anti-reflective stack and positioned on the meta-surface; and - the formation of a metallic trace, part of which is exposed on the first face of the first anti-reflective stack.

[0014] According to one embodiment, the formation of the meta-surface and the first anti-reflective stack comprises: - the formation, on a silicon wafer, of a first stack comprising at least a first layer made of a third material different from the first material, the first stack having a first face corresponding to a first face of the first layer, and a second face opposite the first face and facing the silicon wafer; - the formation, on the first face of the first layer, of the first meta-surface layer; - the formation of second openings through the first layer of meta- surface ; - filling the second openings with a filler material, for example amorphous silicon or polycrystalline silicon, to form the array of pillars, and for example annealing the filler material; - forming a second meta-surface layer of the meta-surface substrate on the first meta-surface layer to cover at least the array of pillars; - removal of the silicon wafer; and - the formation of a second stack comprising at least a second layer on the second face of the first stack, the first stack and the second stack forming the first anti-reflective stack.

[0015] According to one embodiment, the formation of the metal trace with the exposed portion is carried out after the formation of the second meta-surface layer and before the removal of the silicon wafer, and comprises: - the formation of a metallic trace in the meta-surface substrate, for example in the second meta-surface layer; - forming a first opening through the first antireflective stack and the meta-surface substrate to the exposed portion of the metal trace.

[0016] According to one embodiment, the formation of the metal trace with the exposed portion is carried out after the formation of the second meta-surface layer and before the removal of the silicon wafer, and comprises: - the formation of the metallic trace in the second layer of meta-surface; - forming a third meta-surface layer of the meta-surface substrate on the second meta-surface layer to at least cover the metal trace; and - forming a first opening through the first antireflective stack and the meta-surface substrate to the exposed portion of the metal trace.

[0017] According to one embodiment, the method further comprises forming a contact pad in contact with the exposed portion of the metal trace.

[0018] According to one embodiment, the formation of the metal trace with the exposed portion comprises the formation of a metal layer, for example a contact pad, on the first anti-reflective layer, the metal trace corresponding to at least a portion of the metal layer.

[0019] According to one embodiment, the first material is selectively etchable relative to the third material, for example the first material is a silicon oxide and the third material is a silicon nitride.

[0020] According to one embodiment, the pillars are made of polycrystalline silicon and the meta-surface substrate is made of silicon oxide.

[0021] According to one embodiment: - the network of pillars includes first pillars completely crossing the first meta-surface layer, and / or second pillars passing through a partial thickness of the first meta-surface layer; and / or - the pillars have cylindrical or conical shapes with main axes all parallel to each other; and / or - the pillar network comprises pillars having cross-sections of different widths or diameters.

[0022] According to one embodiment, the first antireflection stack and / or the second antireflection stack comprises a stack of dielectric layers with alternating high and low refractive indices, for example layers of silicon oxide or silicon oxynitride alternating with layers of silicon nitride. Brief description of the drawings

[0023] These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which:

[0024] [Fig.lA] and [Fig.lB] are simplified top and cross-sectional views of an example of an optical meta-surface;

[0025] [Fig.2A], [Fig.2B], [Fig.2C], [Fig.2D], [Fig.2E], [Fig.2F], [Fig.2G], [Fig.2H], [Fig.2I], [Fig.2J], [Fig.2K] and [Fig.2L] are perspective and cross-sectional views showing the steps of a method of manufacturing an optical device 200 according to one embodiment;

[0026] [Fig.3A] is a cross-sectional view showing an optical device obtained by the manufacturing method of Figs. 2A to 2L;

[0027] [Fig.3B] is a cross-sectional view showing a variation of the optical device of [Fig.3A];

[0028] [Fig.4] is a top view showing an example of a metal trace of an optical device according to one embodiment; and

[0029] [Fig.5] is a top view showing another example of a metal trace of an optical device according to one embodiment. Description of the embodiments

[0030] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

[0031] For the sake of clarity, only the steps and elements useful for understanding the embodiments described have been shown and are detailed. In particular, not all the components of an optical device are detailed, the embodiments being compatible with the components of usual optical devices, and not all optical devices that can be formed with a meta-structure are detailed.

[0032] Unless otherwise specified, when referring to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be connected by means of one or more other elements.

[0033] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures or to an optical device in a normal position of use.

[0034] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10%, preferably to within 5%.

[0035] In the following description, when reference is made to a lateral dimension, this is a dimension in a plane parallel to the plane of the silicon wafer and / or to the stacking plane of the different layers of the optical device, and when reference is made to a thickness, this is a dimension in a direction substantially perpendicular to the plane.

[0036] Optical devices, such as lenses, diffusers, filters, beam shapers, mirrors, etc., may incorporate an optical meta-surface.

[0037] Optical meta-surfaces are well known to those skilled in the art. An optical meta-surface can be defined as a two-dimensional (2D) surface with small structures distributed and arranged to interact with light in a particular way. The small structures may consist of subwavelength structures, or "meta-atoms." For example, an optical meta-surface, also referred to as an optical meta-structure, may be a surface having a distributed array of nanostructures. The nanostructures may, individually or collectively, interact with light waves. For example, the nanostructures or other meta-atoms may alter a local amplitude, a local phase, or both, of an incoming light wave.

[0038] When the meta-atoms, for example nanostructures, of an optical meta-surface are in a particular arrangement, the optical meta-surface can form, or be part of, an optical device, such as a lens, a filter, a beam shaping device, a diffuser... In some cases, optical meta-surfaces can perform optical functions that are traditionally performed by refractive and / or diffractive optical elements.

[0039] In the following description, an optical meta-surface or an optical meta-structure may be referred to as a "meta-surface".

[0040] In the following description, unless otherwise indicated, when reference is made to a transparent layer or transparent element, it is a layer or element made of a material relatively transparent to light at the wavelengths used or at the wavelengths of interest, for example which has a transmission rate of 90% or more for these wavelengths.

[0041] In the following description, unless otherwise indicated, when reference is made to a glass or a glass substrate, it is an element made of a material relatively transparent to light at the wavelengths used or at the wavelengths of interest, for example which has a transmission rate of 90% or more for these wavelengths. This may be, inter alia, a glass or plastic material.

[0042] In the following description, unless otherwise indicated, when reference is made to a filter, it is an optical filter.

[0043] Figures 1A and 1B are simplified top and cross-sectional views of an exemplary optical meta-surface 100.

[0044] [Fig.lA] illustrates a portion of the meta-surface 100, and [Fig.lB] a portion of a row or column of pillars of the meta-surface 100.

[0045] The meta-surface 100 is a structure formed of a substrate 101, through which pillars 102 are formed. The pillars 102 pass through the substrate 101 and are generally made of a material different from that of the substrate. According to one embodiment, the material of the pillars 102 has an optical index different from that of the material of the substrate 101. According to one example, the pillars 102 pass completely through the substrate 101. According to another example, the pillars 102 pass through a portion of the substrate 101 and their ends are covered by a portion of the substrate or by one or more layers of different materials, such as, for example, etch stop layers and / or anti-reflection layers. The substrate 101 may for example have a thickness of between 10 nm and 10 μm.

[0046] According to one example, the material of the substrate 101 may be selected from the non-exhaustive group comprising: quartz, a compound comprising quartz, silicon, a compound comprising silicon, silicon oxide, silicon nitride, a compound of silicon and carbon, metal oxides of silicon, glass, a compound comprising glass, an aluminum compound, such as an aluminum and arsenic compound, and a gallium compound, such as a gallium and arsenic compound.

[0047] According to one example, the material of the pillars 102 may be chosen from the non-exhaustive group comprising: quartz, a compound comprising quartz, silicon, a a compound comprising silicon, silicon oxide, silicon nitride, a compound of silicon and carbon, metal oxides of silicon, glass, a compound comprising glass, an aluminum compound, such as an aluminum arsenic compound, and a gallium compound, such as a gallium arsenic compound.

[0048] The pillars 102 are generally arranged in the form of a network, that is to say in rows and columns with a regular interval. According to a variant, the pillars 102 are arranged according to a spatial arrangement in which they are spaced at an irregular interval.

[0049] The pillars 102 are generally cylindrical or conical in shape with main axes all parallel to each other and having a cross-section that may have different diameters and different shapes. More particularly, the diameter of a pillar 102 is referred to herein as the diameter of an imaginary circle having the shape of the cross-section of the pillar 102, i.e. the greatest width of the shape of the cross-section of the pillar 102, inscribed in this circle. According to one example, the diameter of a pillar 102 may be between 50 nm and 4 μm. The cross-section of the pillars 102 may have different shapes. In the remainder of the description, the shape of the cross-section of a pillar 102 is referred to as the shape of the cross-section of a pillar 102.

[0050] An optical meta-surface may be used to form all types of optical devices, such as converging lenses, diverging lenses, optical filters, diffusers, etc. To achieve these different optical properties, it may be necessary to use pillars of different diameters and / or shapes in the same structure, and to use an appropriate distribution of these different pillars. In one example, a random distribution of pillars of different diameters may allow a meta-structure with a diffuser function to be created, while a non-random distribution, for example, with a diameter of pillars 102 decreasing or increasing towards a central point of the meta-structure, may allow a converging or diverging lens function to be formed.

[0051] An optical meta-surface can be obtained using an electron beam lithography technique. However, this technique is generally not compatible with mass production.

[0052] An optical meta-surface can be obtained using a nano-imprint lithography technique. Generally, this technique involves forming a layer of imprint resin on a substrate, then pressing a mold having predefined topological patterns onto the substrate with the imprint resin in between, thereby transferring the patterns into the imprint resin, and finally removing the mold. The patterned imprint resin can then be used as an etching mask to etch the corresponding patterns into the substrate. One of the disadvantages of the nano-imprint lithography technique is that it is not possible to etch the corresponding patterns into the substrate. Nanoimprint thography is the use of the mold, which must be changed when the printing resin patterns need to be changed. Therefore, this technique is not easily adaptable to different pattern schemes.

[0053] In order to overcome the disadvantages described above, the fabrication of an optical meta-surface may use techniques and equipment well known in the field of microelectronics, for example, the use of etching, deposition, masking and / or lithography used for the fabrication of microelectronic components. For example, the techniques and equipment for fabricating microelectronic components on a silicon substrate may be used by forming a structure comprising layers, including the meta-surface, on the silicon substrate serving as a fabrication support, transferring the resulting structure to a transparent substrate such as a glass substrate, and then removing the silicon substrate.

[0054] One of the advantages of using these techniques and equipment for the fabrication of optical meta-surfaces is that they use generic materials, which reduces production costs, and that the fabrication is scalable to very high volumes, and therefore compatible with mass production. In addition, microelectronic techniques allow the formation of very small patterns, such as nanometric patterns, for example using high-precision tools such as dry or immersion lithography, to obtain efficient meta-surfaces and form optical devices with high efficiency.

[0055] An optical device incorporating an optical meta-surface may be integrated into an optical sensor module that contains one or more optoelectronic devices, for example at least one light-emitting device, and typically also a light-detecting device. The meta-surface may be used, for example, to modify one or more characteristics, such as phase, amplitude, angle, of a light wave emitted or received as it passes through the meta-surface. For example, the optical device with the meta-surface may be placed above the light-emitting device and the meta-surface may function as a diffuser to reduce to some extent the intensity of a light beam emitted by the light-emitting device, for example for safety reasons, such as protecting a user.However, if the optical device is detached, broken, or removed from the light-emitting device, the light-emitting device is no longer covered and the user is exposed to the full intensity of the light beam. To address this safety issue, the optical device may include a metal trace, or safety trace. Typically, the metal trace is configured to be electrically connected to a voltage rail, and the optical sensor module may include a detection circuit connected to the metal trace and adapted to detect whether the metal trace is connected to, or disconnected from, the voltage rail. If a disconnection is detected, the light-emitting device. light can be cut.

[0056] More generally, the optical device incorporating a meta-surface may include a security device, such as a metal trace, adapted to ensure the safety of the user and / or the integrity of the optical device.

[0057] Previous methods, such as previous methods using microelectronic techniques, generally do not provide an integrated solution for the fabrication of meta-surfaces integrated into optical devices. For example, meta-surfaces may be fabricated by one manufacturer and assembled to optical devices by another manufacturer or assembler, which may pose assembly challenges. For example, the assembly of meta-surfaces into optical devices may be subject to assembly complexity and constraints, such as stress during heat treatment, due to the different materials to be joined, which may pose a reliability problem during assembly.

[0058] Previous methods, such as previous methods using microelectronic techniques, generally do not provide for security devices and, for example, do not provide for electrical connection of these security devices. For example, if the meta-surfaces are manufactured by one manufacturer and assembled to optical devices by another manufacturer or assembler, this may pose a problem of electrical connection of the security devices.

[0059] The inventors propose a method for manufacturing optical devices comprising meta-surfaces, which makes it possible to overcome all or part of the aforementioned drawbacks, in particular to propose an integrated solution for manufacturing meta-surfaces integrated into optical devices, this solution preferably being able to be adapted easily and at low cost to different meta-surface schemes. It would be desirable for this integrated solution to provide safety devices for the protection of the user and / or for the integrity of the optical device, as well as an electrical connection for these safety devices.

[0060] Examples of methods for manufacturing optical devices comprising meta-surfaces and corresponding optical devices will be described below. These embodiments are not limiting and various variations will become apparent to those skilled in the art from the indications of the present description.

[0061] For the sake of simplification, the following description relates to the case where the meta-surface substrate (meta-surface substrate) is made of a silicon oxide, such as silicon dioxide (SiO2), and the pillars of the substrate are made of polycrystalline silicon (polysilicon). However, those skilled in the art will understand that other materials may be used depending on the intended application, for example depending on the optical device and the intended wavelength ranges. The material of the pillars is preferably a material having a refractive index contrast suitable with the meta-surface substrate, e.g. hydrogenated amorphous silicon (a-Si:H).

[0062] Figures 2A, 2B, 2C, 2D, 2E, 2F, 2G, 2H, 2I, 2J, 2K and 2L are perspective and cross-sectional views showing the steps of a method of manufacturing an optical device 200 according to one embodiment.

[0063] In these figures, only a portion of the silicon wafer is shown, it being understood that, in practice, several optical devices are generally formed simultaneously on the silicon wafer, these optical devices then being separated individually by cutting the silicon wafer, for example by sawing.

[0064] [Fig.2A] is a perspective view showing a starting structure comprising a silicon wafer 201 which serves as a support for manufacturing the optical device. A layer 211 of a dielectric material is formed on the silicon wafer 201, and a layer 212 of a dielectric material is formed on the layer 211.

[0065] The layer 211 preferably corresponds to an etch stop layer, for the subsequent step of removing the silicon wafer 201, described below in relation to [Fig.2G]. Therefore, the dielectric material of the layer 211 is preferably selected as a function of the silicon, so that it is not removed when the silicon is removed. The dielectric material of the layer 211 is a transparent material, and can for example be selectively etched with respect to the silicon. The dielectric material of the layer 211 is for example a silicon nitride (SiN).

[0066] Layer 211 may be formed using a chemical vapor deposition (CVD) technique, for example low pressure chemical vapor deposition (LPCVD) or plasma enhanced chemical vapor deposition (PECVD).

[0067] The dielectric material of layer 212 is preferably different from the dielectric material of layer 211. The dielectric material of layer 212 is a transparent material, and preferably a material having an adequate refractive index contrast with layer 211, for example a silicon oxide, such as silicon dioxide (SiO2). Layer 212 may be formed using a CVD technique, for example PECVD.

[0068] Additional layers may be formed on layers 211, 212, or between layers 211 and 212, for example to improve the optical performance of the optical device 200. These additional layers would preferably alternate between materials of different refractive indices, for example to maximize optical transmission at this interface.

[0069] [Fig.2B] is a perspective view showing a structure obtained after: - the formation of a layer 213 of a dielectric material on the layer 212; - forming a layer 202 (first meta-surface layer) of a dielectric material (first material) on the layer 213; and - structuring layer 202 to form openings 202A (second openings) through layer 202; and - filling the openings 202A with a filling material which is preferably different from the dielectric material of the layer 202, to form a set of pillars 203.

[0070] The dielectric material of layer 213 (third material) is preferably different from the dielectric material of layer 212, but may be the same as the dielectric material of layer 211. The dielectric material of layer 213 is a transparent material and preferably a material having an adequate refractive index contrast with layer 212, for example a silicon nitride. Layer 213 may be formed using a CVD technique, for example LPCVD or PECVD.

[0071] Layer 213 preferably corresponds to an etch stop layer, for etching layer 202 in order to form openings 202A. Consequently, the dielectric material of layer 202 (first material) is preferably different from the dielectric material of layer 213 (third material), and preferably capable of being selectively etched relative to the third material, for example to avoid etching layer 213 when layer 202 is etched.

[0072] The dielectric material of layer 202 (first material) is preferably a transparent material, and may be the same as the dielectric material of layer 212, for example a silicon oxide, or may be different, for example a silicon nitride, if the dielectric material of layer 213 is not a silicon nitride. Layer 202 may be formed using a CVD technique, for example PECVD.

[0073] The structuring of the layer 202 uses techniques well known in the field of microelectronics, which are not shown, such as (photo)lithography, etching, deposition and planarization, for example: - forming a lithography mask on the layer 202, the lithography mask comprising openings having shapes and lateral dimensions corresponding to the shapes and lateral dimensions of the pillars to be formed; - etching layer 202 through the openings in the lithography mask to form openings 202A in layer 202, then removing the lithography mask; - depositing a filling layer of the filling material to at least fill the openings 202A; and - optionally, removing any portion of the filler layer remaining on layer 202 using a planarization process, such as polishing chemical-mechanical (CMP).

[0074] The lithography mask defines the shapes of the upper faces of the pillars 203. For example, to manufacture cylindrical or conical pillars, the lithography mask may comprise a grid of circular openings.

[0075] In the example shown, the array of pillars 203 comprises first pillars 203A passing completely through the layer 202, and second pillars 203B passing through a partial thickness of the layer 202. In the example shown, the pillars 203 have a cylindrical or conical shape with main axes all parallel to each other and a cross-section having different diameters. This example is not limiting and other configurations can be envisaged by the person skilled in the art.

[0076] The material (second material) of the pillars 203 and the dielectric material (first material) of the layer 202 are different and preferably have different refractive indices. For example, the material of the pillars 203 may be polycrystalline silicon, and the dielectric material of the layer 202 may be silicon oxide.

[0077] The filling step may be followed by an annealing step, for example if the filling material is an amorphous silicon, in order to form pillars 203 made of polycrystalline silicon. Therefore, the filling material may be different from the final material of the pillars (second material).

[0078] The pillars 203 may be aligned with the upper face of the layer 202 or extend slightly above the upper face of the layer 202.

[0079] The layers 211, 212, 213 form a first stack of a first antireflection stack 210 (illustrated in [Fig.2H]), or antireflection coating. The first stack has an upper face (first face) 213A corresponding to an upper face (first face) of the layer 213 in contact with the layer 202, and a lower face (second face) 211A corresponding to the lower face of the layer 211 in contact with the silicon wafer 201.

[0080] [Fig.2C] is a perspective view showing a structure obtained after: - forming a layer 204 (second meta-surface layer) of a dielectric material on the patterned layer 202 to cover at least the upper faces of the pillars 203; - the formation of a metal trace 205 in the layer 204, preferably from the upper face of the layer 204; and - the protection of the metal trace 205 by a protective layer 206 of a dielectric material preferably different from the dielectric material of the layer 204.

[0081] The dielectric material of layer 204 may be the same as the dielectric material of layer 202, i.e., the first material, for example, a silicon oxide, or may be a different material having the same refractive index as the layer 202. Layer 204 may be formed using a CVD technique, for example PECVD.

[0082] The dielectric material of the protective layer 206 may be the same as the dielectric material of the layer 211 and / or of the layer 213, i.e. the third material, for example a silicon nitride, or may be different. The dielectric material of the protective layer 206 is preferably a material capable of forming a diffusion barrier for the metal of the metal trace 205, for example for copper. Since the surface of the metal trace has a limited footprint, the dielectric material of the protective layer 206 is not necessarily transparent. The protective layer 206 may be formed using a CVD technique, for example LPCVD or PECVD.

[0083] Preferably, the protective layer 206 does not cover the entire upper face of the layer 204. For example, the protective layer 206 forms a strip which covers the metal trace 205 and extends on either side of this metal trace.

[0084] The material of the metallic trace 205 is for example copper (Cu) or any other conductive material, not necessarily transparent.

[0085] The metal trace 205 can be obtained by techniques well known in the field of microelectronics, not shown, such as a so-called Damascene process, that is to say: - forming a lithography mask on the layer 204, the lithography mask comprising an opening having a shape and lateral dimensions corresponding to the shape and lateral dimensions of the metal trace to be formed; - etching layer 204 through the opening in the lithography mask to form an opening through layer 204, then removing the lithography mask; - depositing a metal layer to at least fill the opening of layer 204; and - optionally, removing any portion of the metal layer remaining on layer 204 using a planarization process, such as chemical mechanical polishing (CMP).

[0086] [Fig.2D] is a perspective view showing a structure obtained after the formation of a layer 207 (third meta-surface layer) of a dielectric material on the layer 204 and on the covered metal trace 205.

[0087] The dielectric material of layer 207 is preferably the same as the dielectric material of layer 204 and / or may be the same as the dielectric material of layer 202, i.e., the first material, for example, a silicon oxide. Layer 207 may be formed using a CVD technique, for example PECVD.

[0088] Layer 207 may be designated as a bonding interface layer for subsequent assembly with a glass substrate 208. Bonding interface layer 207 may be thinned and / or planarized prior to subsequent assembly with the glass substrate 208.

[0089] The layers 202, 204, 207 may be called respectively first, second and third meta-surface layers forming a meta-surface substrate 251, and the meta-surface substrate 251 provided with the pillars 203 may be called meta-surface 250, or meta-structure.

[0090] [Fig.2E] is a perspective view showing a structure obtained after forming a glass substrate 208 on the layer 207.

[0091] For example, the glass substrate 208 is bonded by molecular bonding to the bonding interface layer 207.

[0092] The glass substrate 208 may be planarized and / or thinned to a thickness less than or equal to about 210 μm.

[0093] In an advantageous embodiment, the material of the glass substrate 208 and the dielectric material of the layer 207 are similar materials and / or have preferably identical refractive indices, which makes it possible to limit or even eliminate parasitic reflections at the interface between the glass substrate 208 and the layer 207.

[0094] [Fig.2F] is a perspective view showing a structure obtained after the formation of a second antireflective stack 220 on the glass substrate 208.

[0095] The second anti-reflective stack can be called a rear face anti-reflective stack, because it is intended to be positioned on the rear face 200B (second face) of the future optical device 200 (illustrated in [Fig.2L]).

[0096] The second antireflective stack 220 may be a stack of dielectric layers with alternating high and low refractive indices, for example, layers of silicon oxide or silicon oxynitride (SiON) alternating with layers of silicon nitride (SiN).

[0097] By way of non-limiting example, the second anti-reflective stack 220 may comprise: - a first antireflective (AR) layer 221 of silicon oxide or silicon oxynitride on the glass substrate 208; - a second anti-reflective (AR) layer 222 of silicon nitride on the first AR layer 221; - a third antireflective (AR) layer 223 of silicon oxide or silicon oxynitride on the second AR layer 222; - a fourth anti-reflective (AR) layer 224 of silicon nitride on the third AR layer 223; - a fifth antireflective (AR) layer 225 of silicon oxide or silicon oxynitride on the fourth AR layer 224; - a sixth antireflective (AR) layer 226 of silicon nitride on the fifth AR layer 225; and - a seventh antireflective (AR) layer 227 of silicon oxide or silicon oxynitride on the sixth AR layer 226.

[0098] The antireflective layers may be formed using a CVD technique, for example PECVD.

[0099] The second anti-reflective stack 220 may allow maximizing optical transmission, for example by minimizing Fresnel reflection on the glass substrate 208.

[0100] Other configurations of the second antireflective stack 220, such as another number of layers, and / or other dielectric materials and / or combinations of materials, and / or thicknesses, may be envisaged by those skilled in the art, for example to maximize optical transmission in the wavelengths of interest, over the range of incidence angles appropriate and adapted to the tools available for manufacturing.

[0101] [Fig.2G] is a perspective view showing a structure obtained after turning over the structure of [Fig.2F] and removing the silicon wafer 201.

[0102] The silicon wafer 201 may be removed by grinding, for example by grinding off a large portion of the thickness of this silicon wafer, then polishing the remaining portion of this silicon wafer down to layer 211, which may be selected to stop polishing.

[0103] Optionally, a temporary silicon support 209 may be assembled or bonded to the second antireflection stack 220, before or after the structure of [Fig.2F] is turned over, and preferably before the silicon wafer 201 is removed. The temporary silicon support 209 may be used to reinforce the structure when the silicon wafer 201 is removed. For example, the temporary silicon support 209 is bonded to the second antireflection stack 220 using a dry adhesive film 209A with a thickness of 65 μm for example.

[0104] [Fig.2H] is a perspective view showing a structure obtained after forming a layer 214 of a dielectric material on the layer 211.

[0105] The dielectric material of layer 214 is preferably different from the dielectric material of layer 211, and is for example silicon dioxide or silicon oxynitride. Layer 214 may be formed using a CVD technique and may be a low temperature oxide (LTO).

[0106] The layer 214 can form, with the first stack of layers 211, 212, 213, the first antireflection stack 210. The layers 214, 211, 212, 213 can be called respectively first antireflection layer, second antireflection layer, third antireflective layer and fourth antireflective layer of the first antireflective stack 210. The upper face 21 OA (first face) of the first antireflective stack 210 corresponds to the upper face of the layer 214.

[0107] Instead of a layer 214, it could be a stack of layers (second stack).

[0108] The first anti-reflective stack 210 can be called a front face anti-reflective stack, because it is intended to be positioned on the front face 200A (first face) of the future optical device 200 (illustrated in [Fig.2L]).

[0109] Other configurations of the first antireflection stack 210, such as another number of layers and / or other dielectric materials and / or combinations of materials and / or thicknesses, may be envisaged by those skilled in the art, for example to maximize optical transmission in the wavelengths of interest, over the range of appropriate angles of incidence and adapted to the available manufacturing tools. The first antireflection stack is preferably a stack of dielectric layers with alternating high and low refractive indices.

[0110] The first antireflection stack 210 may be configured to correct an angle of incidence of the light rays reaching the array of pillars. For example, the first antireflection stack 210 may be configured to correct the initial angle of incidence of the light rays relative to the normal of the front face 200A of the optical device 200 so as to rectify the initial incident light rays so that the angle of the rays incident on the array of pillars is as close as possible to the normal.

[0111] Figures 21, 2J and 2K are cross-sectional views in the direction AA illustrated in [Fig.2H], showing examples of electrical connection steps of the metal trace 205 which is incorporated in the layers 202, 204, 207, in other words in the meta-surface substrate 251.

[0112] [Fig.21] illustrates a structure obtained after the deposition of a resin mask 240 on the upper face 210A (first face) of the first antireflection stack 210. The resin mask 240 preferably covers the array of pillars 203 and has an opening 241 which is positioned above the metal trace 205, away from the array of pillars 203.

[0113] [Fig.2J] illustrates a structure obtained after etching the first antireflection stack 210 and the layers 202, 204, 207, i.e., the meta-surface substrate 251, through the opening 241 of the resin mask 240 to the metal trace 205, in order to form an opening 242 (first opening) through the first antireflection stack 210 and the meta-surface substrate 251, and to access the metal trace 205. The resin mask 240 is then removed. The metal trace 205 then comprises a portion 205A which is exposed at the upper face 210A of the first em- 210 anti-reflective coating.

[0114] [Fig.2K] represents a structure obtained after deposition of a contact pad 230, or metallization on pad, on the first antireflection stack 210 and in the opening 242, in order to connect the exposed part 205A of the metal trace 205. The contact pad 230 follows the shape of the upper face of the structure of [Fig.2J], and therefore comprises a hollow 230A which corresponds substantially to the opening 242.

[0115] [Fig.2L] is a perspective view showing the optical device 200 obtained after the formation of the contact pad 230, the temporary silicon support 209 not having been removed yet (the final optical device does not include this temporary silicon support). For the sake of simplification, [Fig.2L] does not show the recess 230A of the contact pad 230 which is shown in the cross-sectional view of [Fig.2K].

[0116] The contact pad 230 may comprise several layers, for example: - a first metal layer 231, for example a titanium (Ti) layer on the first antireflection stack 210: the first metal layer 231 preferably acts as an adhesion interface layer with the first antireflection stack 210, for example with the layer 214 which may be a silicon dioxide or oxynitride layer, and / or as a metal diffusion barrier; - a second metal layer 232, for example a layer of a titanium and tungsten alloy (TiW), on the first metal layer 231: the second metal layer 232 preferably also acts as an adhesion interface layer and / or as a metal diffusion barrier; - a third metal layer 233 to form an electrical contact, for example a gold layer, on the second metal layer 232.

[0117] The described manufacturing method shows the advantages of such an integrated method, which is suitable for forming an optical device by forming a meta-surface, positioning a glass substrate on the meta-surface and forming the front-side and back-side anti-reflection stacks respectively on the meta-surface and on the glass substrate, using microelectronic techniques and equipment. The integrated manufacturing method makes it possible to form precise patterns and thus a high-resolution optical device, to adapt to different meta-surface schemes and to reduce costs. Furthermore, the integrated manufacturing method makes it possible to form an electrical contact through the first anti-reflection stack, for example to connect a security trace in the meta-surface.

[0118] [Fig. 3A] is a cross-sectional view showing an optical device 200 obtained by the manufacturing method of FIGS. 2A to 2L, after removal of the temporary silicon support 209. [Fig. 3B] is a cross-sectional view showing a variant of the optical device of [Fig. 3A].

[0119] For the sake of simplification, the contact pad 230 is not shown in the figures. 3A and 3B.

[0120] The optical device 200 of [Fig.3A] corresponds substantially to the optical device of [Fig.2L], without the contact pad 230 being shown, and without the temporary silicon support 209 which has been removed.

[0121] The optical device 200 therefore comprises: - a meta-surface 250 having an upper face 250A (first face) and a lower face 250B (second face); - a first anti-reflective stack 210 covering the upper face 250A of the meta-surface 250, the first anti-reflective stack having an upper face 210A (first face) opposite a lower face 210B (second face) which faces the meta-surface; - a glass substrate 208 having an upper face 208A (first face) covered by the meta-surface 250 and a lower face 208B (second face) opposite the first face; - a second anti-reflective stack 220 covered by the lower face 208B of the glass substrate 208.

[0122] The meta-surface 250 comprises an array of pillars 203, as well as a metal trace 205, embedded in the meta-surface substrate 251. Although not shown in [Fig.3A], but in [Fig.2J], a portion 205A of the metal trace 205 is exposed on the upper face 210A of the first anti-reflective stack 210 by means of an opening 242 in the first anti-reflective stack 210 and the meta-surface substrate 251 extending to this portion of the metal trace.

[0123] A non-limiting example of the materials and thickness ranges of the different layers and elements of the optical device 200 of [Fig.3A] is given in the following Table 1:

[0124] [Tables 1] Layer or Element Reference Material Example Thickness Ranges 214 SiO2 layer 110-150 nm 211 SiN layer 10-20 nm 212 SiO2 layer 40-60 nm 213 SiN layer 45-65 nm 203 polysilicon pillars 550-850 nm (higher thickness) 251 SiO2 metasurface substrate 1-2 pm 205 Cu metal trace 150-250 nm 210 glass substrate glass 150-250 pm 221 SiON layer 15-30 nm 222 SiN layer 20-35 nm 223 SiON layer 80-130 nm 224 SiN layer 15-25 nm 225 SiON layer 25-45 nm 226 SiN layer 60-90 nm layer 227 SiON 70-110 nm

[0125] The optical device 300 of [Fig. 3B] differs from the optical device of [Fig. 3A] in that the meta-surface 350 does not include a metal trace and the meta-surface substrate 351 does not include the third meta-surface layer, i.e., layer 207 of [Fig. 3A]. Therefore, the meta-surface substrate 351 of the optical device 300 of [Fig. 3B] has a thickness less than that of the meta-surface substrate 351 of the optical device 200 of [Fig. 3A].

[0126] A non-limiting example of the materials and thickness ranges of the different layers and elements of the optical device 300 of [Fig.3B] is given in the following Table 2:

[0127] [Tables2] Layer or Element Reference Material Example Thickness Ranges 214 SiO2 layer 110-150 nm 211 SiN layer 10-20 nm 212 SiO2 layer 40-60 nm 213 SiN layer 45-65 nm 203 Polysilicon pillars 550-850 nm (higher thickness) 351 SiO2 meta-surface substrate 0.5-1.5 pm 210 Glass substrate glass 150-250 pm 221 SiON layer 15-30 nm 222 SiN layer 20-35 nm 223 SiON layer 80-130 nm 224 SiN layer 15-25 nm 225 SiON layer 25-45 nm 226 SiN layer 60-90 nm 227 SiON 70-110 nm

[0128] The meta-surface 250 of figures 2D to 2L and of [Fig.3A] comprises, for example incorporates, the metal trace 205 of which a part 205A is exposed on the upper face 210A of the first anti-reflective stack 210.

[0129] According to a variant, the metal trace may not be included or incorporated into the meta-surface 350, as in the example of [Fig. 3B]. In this variant, the metal trace may be formed by at least a portion of a contact pad, such as the contact pad 230 of [Fig. 2L], which is exposed on the front face of the optical device, i.e., on the upper face of the first antireflection stack. The metal trace may be formed, for example, by at least a portion of a gold layer corresponding to an upper layer of the contact pad, such as the gold layer 233 of [Fig. 2L]. The contact pad, for example the gold layer, may be patterned to form the metal trace.

[0130] [Fig.4] is a top view showing an example of a metal trace 405 of an optical device according to one embodiment. In this example, the metal trace 405 is incorporated into the meta-surface 450. The optical device is by example the optical device 200 of [Fig.2L] and / or of [Fig.3A].

[0131] The metal trace 405 of [Fig.4] has a zigzag shape and is connected at its ends to conductive pads 401. The conductive pads may be exposed on the front face of the optical device, i.e. on the upper face of the first antireflection stack. This shape is not limiting and other shapes may be envisaged by the person skilled in the art.

[0132] [Fig. 5] is a top view showing another example of a metal trace 505 of an optical device according to one embodiment. In this example, the metal trace 505 is not included or incorporated into the meta-surface. The optical device is for example the optical device 300 of [Fig. 3B].

[0133] The metal trace 505 is formed by a metal layer exposed on the front face of the optical device, i.e. on the upper face of the first antireflection stack, for example a gold layer of a contact pad, which is shaped to form the metal trace. The metal trace 505 of [Fig.5] has an omega shape. This shape is not limiting and other shapes can be envisaged by the person skilled in the art.

[0134] The metal trace 505 is connected at its ends to conductive pads 501.

[0135] More generally, and whatever its location, the metallic trace comprises preferably conductive contacts, such as conductive pads, which are configured to be at a fixed voltage, e.g. electrically connected, or bonded, to a voltage rail.

[0136] A detection circuit may be connected to the metal trace, the detection circuit being adapted to detect whether the metal trace is connected to, or disconnected from, the voltage rail. If a disconnection is detected, an action such as turning off a light emitting device covered by the optical device may be performed.

[0137] The optical device with the meta-surface may be integrated into an optical sensor module containing one or more optoelectronic devices, for example at least one light emitting device, and generally also a light detecting device. The meta-surface of the optical device may be used, for example, to modify one or more characteristics, such as phase, amplitude, angle, of an emitted or incoming light wave as it passes through the meta-surface.

[0138] The optical device with the meta-surface may be placed above the light-emitting device. For example, the meta-surface may function as a diffuser to reduce to some extent the intensity of a light beam emitted by the light-emitting device, and the metal trace may be used to detect whether the optical device is detached, broken, or otherwise removed from the light-emitting device, and if so, the light-emitting device may be cut off.

[0139] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art.

[0140] Finally, the practical implementation of the embodiments and variants described is within the reach of those skilled in the art from the functional indications given above.

Claims

Claims

1. An optical device (200; 300) comprising: - a meta-surface (250; 350) comprising a meta-surface substrate (251; 351) having at least a first meta-surface layer (202) of a first material, and an array of pillars (203) across the first meta-surface layer (202), the pillars being made of a second material different from the first material, the meta-surface having a first face (250A; 350A) and a second face (250B; 350B) opposite the first face of said meta-surface; - a first anti-reflection stack (210) having a first face (210A) and a second face (210B) opposite the first face of said first anti-reflection stack and positioned on the first face (250A; 350A) of the meta-surface; and - a metal trace (205; 405; 505) having a portion exposed at the first face of the first anti-reflective stack.

2. An optical device according to claim 1, wherein the first meta-surface layer (202) extends over the first face (250A) of the meta-surface (250).

3. An optical device according to claim 1 or 2, wherein the metal trace (205) is included, for example embedded, in the meta-surface substrate (251), the optical device comprising a first aperture (242) extending deep through the first anti-reflection stack (210) and the meta-surface substrate to the exposed portion of the metal trace.

4. An optical device according to claim 3, wherein the metal trace (205) is embedded in a second meta-surface layer (204) of the meta-surface substrate (251) in contact with the first meta-surface layer (202), the meta-surface substrate further comprising a third meta-surface layer (204) in contact with the second meta-surface layer (204) and covering the metal trace, the second meta-surface layer being between the first meta-surface layer and the third meta-surface layer.

5. Optical device according to claim 1 or 2, wherein the metal trace (505) is positioned on the first face (210A) of the first anti-reflection stack (210), for example corresponds to at least part of a contact pad (230).

6. An optical device according to any one of claims 1 to 5,

7.

8.

9. further comprising a transparent substrate (208), for example a glass substrate, the second face (250B) of the meta-surface being on a first face (208A) of the transparent substrate. An optical device according to claim 6, further comprising a second anti-reflective layer (220), a second face (208B) of the transparent substrate, opposite the first face of said transparent substrate, being located on said second anti-reflective layer. A method of manufacturing an optical device (200; 300), comprising: - forming a meta-surface (250; 350) comprising a meta-surface substrate (251; 351) including at least a first meta-surface layer (202) of a first material, and an array of pillars (203) across the first meta-surface layer (202), the pillars being made of a second material different from the first material, the meta-surface having a first face (250A; 350A) and a second face (250B; 350B) opposite the first face of said meta-surface; - forming a first anti-reflective stack (210) on the first face (250A; 350A) of the meta-surface, the first anti-reflective stack having a first face (210A) and a second face (210B) opposite the first face of said first anti-reflective stack and positioned on the meta-surface; and - the formation of a metallic trace (205; 405; 505) of which a part is exposed on the first face of the first anti-reflective stack. The method of claim 8, wherein forming the meta-surface (250; 350) and the first anti-reflective stack (210) comprises: - the formation, on a silicon wafer (201), of a first stack (211, 212, 213) comprising at least a first layer (213) made of a third material different from the first material, the first stack having a first face corresponding to a first face (213A) of the first layer, and a second face (211B) opposite the first face and facing the silicon wafer; - the formation, on the first face (213A) of the first layer (213), of the first meta-surface layer (202); - forming second openings (202A) through the first meta-surface layer (202); - filling the second openings with a filling material, for example amorphous silicon or polycrystalline silicon, to form the array of pillars (203), and for example annealing the filling material; - forming a second meta-surface layer (204) of the meta-surface substrate on the first meta-surface layer (202) to at least cover the pillar array (203); - removing the silicon wafer (201); and - forming a second stack comprising at least a second layer (214) on the second face (21 IA) of the first stack (211, 212, 213), the first stack and the second stack forming the first anti-reflective stack (210).

10. The method of claim 9, wherein the formation of the metal trace with the exposed portion is performed after the formation of the second meta-surface layer (204) and before the removal of the silicon wafer, and comprises: - forming a metal trace (205) in the meta-surface substrate (251), for example in the second meta-surface layer (204); - forming a first opening (242) through the first anti-reflective stack and the meta-surface substrate to the exposed portion of the metal trace.

11. The method of claim 9, wherein forming the metal trace (205) with the exposed portion is performed after forming the second meta-surface layer (204) and before removing the silicon wafer, and comprises: - forming the metal trace (205) in the second meta-surface layer (204); - forming a third meta-surface layer (207) of the meta-surface substrate on the second meta-surface layer (204) to at least cover the metal trace; and - forming a first opening (242) through the first anti-reflective stack (210) and the meta-surface substrate to the exposed portion of the metal trace.

12. The method of claim 10 or 11, further comprising forming a contact pad (230) in contact with the exposed portion of the metal trace.

13. The method of claim 9, wherein forming the metal trace (505) with the exposed portion comprises forming a metal layer, e.g., a contact pad, on the first antireflective layer, the metal trace corresponding to at least one part of the metal layer.

14. A method according to any one of claims 9 to 13, wherein the first material is selectively etchable relative to the third material, for example the first material is a silicon oxide and the third material is a silicon nitride.

15. An optical device according to any one of claims 1 to 7, wherein the pillars (203) are made of polycrystalline silicon, and the meta-surface substrate (251; 351) is made of silicon oxide.

16. An optical device according to any one of claims 1 to 7 and 15, wherein: - the array of pillars (203) comprises first pillars (203A) passing completely through the first meta-surface layer (202), and / or second pillars (203B) passing through a partial thickness of the first meta-surface layer (202); and / or - the pillars (203) have cylindrical or conical shapes with main axes all parallel to each other; and / or - the array of pillars (203) comprises pillars (203) having cross-sections of different widths or diameters.

17. An optical device according to any one of claims 1 to 7, 15 and 16, wherein the first antireflection stack (210) and / or the second antireflection stack (220) comprises a stack of dielectric layers with alternating high and low refractive indices, for example layers of silicon oxide or silicon oxynitride alternating with layers of silicon nitride.

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