OPTICAL FILTERING DEVICE COMPRISING FABRY-PEROT CAVITIES WITH STRUCTURED LAYERS AND DIFFERENT THICKNESSES

Abstract

Filtering device (100) comprising at least first and second interference filters (106) each comprising at least one Fabry-Perot cavity formed by semi-reflective layers (108, 118) between which at least one structured layer (110) is arranged, wherein: - the structured layer is common to the first and second filters, - the structured layer has a substantially constant thickness, - the structured layer comprises at least two materials of different refractive indices included in each of the cavities, and - the cavity of the second filter comprises at least one spacer (120) arranged between one of the semi-reflective layers and the structured layer such that a distance between the semi-reflective layers of the cavity of the second filter is greater than a distance between the semi-reflective layers of the cavity of the first filter. Figure for abstract: 1

Description

Title of the invention: OPTICAL FILTERING DEVICE COMPRISING FABRY-PEROT CAVITIES WITH A STRUCTURED LAYER AND DIFFERENT THICKNESSES TECHNICAL FIELD AND PRIOR ART

[0001] The invention relates to an optical filtering device comprising interference filters with Fabry-Perot cavities, advantageously used in the field of multispectral or hyperspectral imaging.

[0002] An image sensor typically comprises a matrix of filters centered on wavelengths that are different from one another. In a conventional color image sensor, this matrix of filters corresponds to a Bayer matrix formed by red, green, and blue filters that allow the colorimetry of the scene to be reconstructed. These filters are made of colored resins and pixelated directly on the sensor.

[0003] In a hyperspectral camera, filters are also organized in a matrix but are present in greater numbers (typically 5 to 10, or even more), so as to detect the spectral signature of objects in a scene. The information returned by this type of camera is richer and the applications are numerous in industrial vision, in the military or environmental field, for example for gas detection. The filters are not made with colored resins, in particular because it is difficult to obtain resins centered on wavelengths other than those of the colors red, green and blue, and also because the spectral responses of the resins are too broad compared to those sought for the filters of a hyperspectral camera.

[0004] An interference filter wheel, placed in front of the sensor, and therefore not integrated into it, is for example used in a hyperspectral camera. For each acquisition, a different filter is placed in front of the sensor. The different acquisitions made are then combined to obtain the final image.

[0005] In addition to the disadvantage linked to the non-integration of the filters with the sensor, given that different acquisitions are necessary to obtain the filtered images according to the different spectral responses of the filters located on the wheel, this technology has limitations for real-time applications.

[0006] Wavelength filtering can be achieved by interference filters of the Fabry-Perot type, or Fabry-Perot cavity filters. The principle of such filters is for example described in the work of HA MacLeod, “Thin film optical filters III”, Institute of Physics Publishing, London, 2001, pages 260-263. A Fabry-Perot cavity comprises two semi-reflective layers, or semi-reflecting mirrors, arranged in facing each other and between which there is a medium of refractive index, or optical index, n, for example a layer of material of refractive index n. The incident light is reflected by the filter for all wavelengths, except for a discrete set of wavelengths which are transmitted out of the filter. For these transmitted wavelengths, the optical path traveled by the light during a round trip in the Fabry-Perot cavity is a multiple of 2ir. At normal incidence, these wavelengths, or central wavelengths of the spectral responses of the filters, are therefore a function of the refractive index n and a thickness d of the layer of material located between the two semi-reflecting layers. The central wavelengths Xm at the different orders m of the Fabry-Perot cavity are defined by the following equation: 2W (1)

[0007] with m corresponding to the order of the Fabry-Perot cavity considered, and <pa et <pb correspondant aux déphasages se produisant dans la cavité lors des réflexions sur les couches semi-réflectrices.

[0008] Documents WO 2013 / 064511 Al and “Monolithic integration of flexible spectral filters with CMOS image sensors at wafer level for low cost hyperspectral imaging” by M. Jayapala et al., IISW2013, describe Fabry-Perot cavity filters whose wavelength tunability is achieved by varying the thickness of the cavity of each of the filters. This is a so-called “staircase” filter technology. Sixteen to thirty-two filters are thus produced within a sensor adapted for the 600 nm - 1000 nm range, thus covering a small part of the visible range and the near infrared range. The layers of material located between the semi-reflective layers are made of amorphous silicon or SiO2. The semi-reflective layers are made of stacks of alternating layers of amorphous silicon and SiO2 common to all filters.The lower part of the visible range, i.e. wavelengths between approximately 400 nm and 600 nm, is inaccessible for these filters because the absorption coefficient of amorphous silicon is too high at these wavelengths. The integration of the filters is monolithic, i.e. carried out directly on the sensor by deposition and etching steps following the back-end steps of the sensor.

[0009] This type of filtering device has two drawbacks:

[0010] - the number of engraving steps to be performed increases with the number of filters desired, whatever the production process envisaged for this staircase structure;

[0011] - the most economical production method in terms of the number of etching steps (N steps etching for 2N filters) consists of carrying out successive partial etchings in the same layer. However, in a collective manufacturing process (on the wafer scale), the deposition and partial etching steps are always affected by a certain degree of non-uniformity on the surface of the wafer whose diameter is equal to 200 mm or 300 mm. The central wavelength of the spectral responses of the filters is very sensitive to the thickness of the cavity. Document WO 2013 / 064511 A1 specifies that a thickness control of ± 2% is essential. This type of filtering device is therefore not ideal for industrialization requiring collective manufacturing of filters, in particular because the errors induced by the successive etching steps can accumulate.

[0012] Document US 7,759,679 B2 describes a filtering device in which the wavelength tunability of the filters is achieved by varying the effective refractive index of the medium located between the two semi-reflective layers of the cavity, the thickness of this medium being constant in all the filters. For this, nanostructures are etched in a layer based on a first dielectric material. The etched areas are filled with a second dielectric material whose refractive index is, for example, lower than that of the first dielectric material, and chemical-mechanical polishing (CMP) is carried out to planarize the layer comprising the nanostructures.The light passing through these nanostructures sees an average refractive index, or effective refractive index, whose value is between those of the refractive indices of the two dielectric materials because the lateral dimensions of the nanostructures are smaller than the wavelengths intended to be transmitted by the filter. From a single mask, it is possible to vary the dimensions of these nanostructures in the plane of the layer, and therefore to vary the effective refractive index along this structured layer in a range between the refractive index of the second dielectric material and the refractive index of the first dielectric material. All the desired filters within the structured layer can therefore be produced with the implementation of a single lithography and etching step.The process for producing this filtering device does not involve partial etching and therefore does not have the disadvantages associated with producing “step” filters.

[0013] However, the spectral range accessible for such a filtering device is limited by the difference between the refractive indices of the materials used to make the structured layer. However, in the visible and near infrared ranges, there are no very large index differences between the different known materials that can be used. Thus, for order 1 of Fabry-Perot cavities, it is possible to tune the filters between 450 nm and 680 nm only, using SiO2 (refractive index equal to 1.47) as a low index material and making it possible to produce a filter whose spectral response is centered at 450 nm when this filter only contains SiO2, and TiO2 (refractive index equal to 2.25) as a high index material and making it possible to produce a filter whose spectral response is centered at 680 nm when this filter only contains TiO2. Such a filtering device therefore does not allow multispectral filtering to be carried out on the entire visible and near infrared ranges simultaneously.

[0014] Document US 2011 / 0290982 A1 describes a filtering device in which the same structuring principle is used to tune the filters by the effective refractive index of the layer of materials located between the semi-reflective layers. Better selectivity, and in particular better rejection of the filters, is obtained by using two Fabry-Perot cavities superimposed on each other for each of the filters. To facilitate the production of the patterns in the case where the nanostructures are small compared to the resolution accessible in lithography, it is proposed in this document to produce, instead of very fine patterns with etching throughout the thickness of the structured layer, wider patterns but over a smaller depth so as to obtain the same effective index.The volume proportions of the two materials are in this case the same as for engraving through the entire thickness of the material for very fine patterns. The physical thickness of the cavity, defined by the distance between the semi-reflective layers corresponding to metal layers, also remains constant.

[0015] As for document US 7,759,679 B2, the spectral range accessible with this type of device is limited by the index difference between the two dielectric materials used. In addition, when nanostructures are produced through only a part of the thickness of the layer, it is necessary, to achieve the same wavelength ranges, to produce two nanostructured layers one on top of the other, inside each of the Fabry-Perot cavities. This increases the complexity and the cost of producing the filtering device because each nanostructured layer requires a high-resolution lithography step. Furthermore, the etching of the second nanostructured layer can degrade, by overetching, the first nanostructured layer with such a method. Statement of the invention

[0016] An aim of the present invention is to propose an optical filtering device solving at least in part the problems of the filtering devices of the prior art set out above.

[0017] For this, the present invention proposes an optical filtering device comprising at least first and second interference filters each comprising at least a first Fabry-Perot cavity formed by first and second semi-reflective layers between which at least one first structured layer is arranged, in which:

[0018] - the first structured layer is common to the first and second filters interferential,

[0019] - the first structured layer has a substantially constant thickness,

[0020] - the first structured layer comprises at least two materials with indices of different refractions included in each of the first Fabry-Perot cavities, and

[0021] - the first Fabry-Perot cavity of the second interference filter comprises at at least one first spacer disposed between one of the first and second semi-reflective layers and the first structured layer such that a distance between the first and second semi-reflective layers of the first Fabry-Perot cavity of the second interference filter is greater than a distance between the first and second semi-reflective layers of the first Fabry-Perot cavity of the first interference filter.

[0022] The expression "structured layer" designates the fact that the layer comprises portions of the two materials of different refractive indices which form structures, or patterns, within the layer.

[0023] Such an optical filtering device therefore proposes the production of several interference filters with Fabry-Perot cavities whose central wavelengths are defined by several parameters linked to the structured layer (the values ​​of the refractive indices of the two materials used, the parameters, such as the shape and dimensions, of the patterns formed by the two materials, the thickness of the structured layer) but also, for the second interference filter(s), by several parameters linked to the spacer present in the Fabry-Perot cavities of the second interference filter(s) (refractive index of the material of the spacer, its thickness, etc.).

[0024] Thus, compared to the filtering devices of the prior art using only a structured layer of constant thickness, the optical filtering device according to the invention is suitable for carrying out filtering in a wider range of wavelengths, which can cover for example the visible range and the near infrared, and in particular which is not limited by the nature of the materials used to produce the structured layer, thanks to the presence of the spacer in the second interference filter(s).

[0025] Compared to a staircase optical filtering device, the optical filtering device according to the invention can be produced with a much lower number of etching steps, without resorting to partial etching steps. The optical filtering device according to the invention is therefore well suited for collective manufacturing of filters at the substrate or wafer scale, without errors induced by successive partial etching steps.

[0026] The optical filtering device according to the invention also comprises a structure suitable for integration on a sensor, for example a CMOS type image sensor, allowing real-time capture across the entire range of spectral responses of the interference filters of the optical filtering device.

[0027] Each of the interference filters can transmit a single spectral band (each interference filter therefore being of the band-pass type) for example in the complete range of the visible and near infrared domain, thus facilitating the processing of images captured via a sensor equipped with such an optical filtering device.

[0028] The optical filtering device may cover only the visible range, for example when the materials that can be used to form the structured layer have refractive indices of similar values. In another configuration, the optical filtering device may cover at least part of the visible range and / or at least part of the infrared range (near infrared and / or mid infrared and / or far infrared) and / or at least part of the UV range. The second interference filter(s) may in particular perform filtering in the infrared range, the first interference filter(s) being able to be dedicated to the visible and / or UV range.

[0029] The Fabry-Perot cavities can be arranged on a transparent substrate, for example made of glass. Such a transparent substrate can allow integration of the optical filtering device on a sensor, for example by transfer onto a silicon substrate.

[0030] The optical filtering device may comprise a single structured layer common to the first Fabry-Perot cavities of all the interference filters of the device and located inside the first Fabry-Perot cavities. Such a configuration is advantageous because the use of a single structured layer per Fabry-Perot cavity simplifies and reduces the cost of production compared to Fabry-Perot cavities comprising several superimposed structured layers, and also makes it possible to avoid possible degradation of the lower structured layer during the production of the upper structured layer. In addition, the presence of the spacer in the second interference filter(s) allows the optical filtering device to cover a spectral range at least as wide as that covered by a filtering device not comprising a spacer but using one or more superimposed structured layers.

[0031] The spacer may be disposed on or under the structured layer.

[0032] The first structured layer is advantageously continuous from one Fabry-Perot cavity to another. In other words, the main faces of the parts of the structured layer arranged in the different cavities are arranged in two planes only.

[0033] The spectral responses of the interference filters can cover a large, substantially continuous spectral band (each interference filter being able to form a band-pass filter allowing a range of wavelengths to pass adjacent to a range of wavelengths that another adjacent filter allows to pass) or several distinct spectral bands that are not necessarily adjacent.

[0034] The two materials with different refractive indices may correspond to dielectric and / or semiconducting materials. Similarly, the first spacer may comprise at least one dielectric or semiconducting material.

[0035] The first structured layer may comprise periodic patterns formed by portions of a second of the two materials of different refractive indices arranged in a first of the two materials of different refractive indices.

[0036] In each of the first Fabry-Perot cavities, values ​​of dimensions (dimensions in a principal plane of the structured layer) and of a period of the periodic patterns may be less than a value of a central wavelength of a spectral response of said first Fabry-Perot cavity at order 1.

[0037] The periodic patterns can form, in a main plane of the first structured layer, two-dimensional structures, for example rectangular or square-shaped pads. The periodic patterns are in this case well suited to filtering unpolarized light or light comprising two polarizations.

[0038] Alternatively, the periodic patterns may form, in the main plane of the first structured layer, one-dimensional structures, for example slits extending in a single direction. The periodic patterns are in this case well suited to filtering light having a single polarization.

[0039] Advantageously, the portions of the second of the two materials with different refractive indices can be formed throughout the thickness of the first structured layer.

[0040] It is however possible that the portions of the second of the two materials with different refractive indices are formed in only a part of the thickness of the first structured layer. In this case, the presence of the spacer in the second interference filter(s) makes it possible to cover a large spectral band without necessarily having to use two structured layers superimposed within the Fabry-Perot cavities.

[0041] The optical filtering device may further comprise at least one etching stop layer disposed at least between one of the first and second semi- reflectors and the first structured layer of the first Fabry-Perot cavity of the first interference filter. This etch stop layer may in particular protect the structured layer during the production of the spacer which may involve a step of etching material present on the first interference filter(s). This etch stop layer may have significant etching selectivity compared to that of the material forming the spacer. A single etch stop layer may be sufficient to guarantee the integrity of the structured layer common to all the filters. It is possible for this etch stop layer to also be present at the level of the second interference filter(s), which simplifies the production of this etch stop layer without causing any disturbance in the filtering carried out.

[0042] The first interference filter and / or the second interference filter may comprise at least one second Fabry-Perot cavity superimposed on the first Fabry-Perot cavity. Compared to an interference filter comprising a single Fabry-Perot cavity, the superposition of two Fabry-Perot cavities, advantageously identical to one another, makes it possible to obtain better rejection of the filter and a spectral response whose sides have a greater slope, and therefore a more precise range of transmitted wavelengths. In addition, this configuration makes it possible to have greater uniformity, in terms of maximum transmission, of the spectral responses of the interference filters over the entire range of targeted wavelengths.

[0043] In this configuration, one of the two semi-reflective layers of the first Fabry-Perot cavity can also form one of the two semi-reflective layers of the second Fabry-Perot cavity.

[0044] When the second interference filter comprises a second Fabry-Perot cavity, said second Fabry-Perot cavity may comprise at least one second spacer arranged between a third semi-reflective layer and a second structured layer of said second Fabry-Perot cavity.

[0045] The second spacer may comprise at least one dielectric or semiconducting material.

[0046] The optical filtering device may further comprise at least one portion of material absorbing wavelengths of values ​​lower than that of a central wavelength of a spectral response of the first Fabry-Perot cavity of the second interference filter, for example amorphous or polycrystalline silicon, arranged on or in the first Fabry-Perot cavity of the second interference filter. This portion of material makes it possible in this case to absorb certain wavelengths transmitted at order 2 (or at orders higher than 2) of the Fabry-Perot cavity of the second interference filter.

[0047] The first spacer and / or the second spacer may comprise amorphous or polycrystalline silicon, which allows them to also act as an absorbent material as described above.

[0048] The optical filtering device may comprise several first interference filters arranged next to each other and in which volume proportions of the two materials with different refractive indices relative to each other may be different from one first interference filter to another, and / or may comprise several second interference filters arranged next to each other and in which volume proportions of the two materials with different refractive indices relative to each other may be different from one second interference filter to another.

[0049] The volume proportions of the two materials with different refractive indices relative to each other in the second interference filter(s) may be different from the volume proportions of the two materials with different refractive indices relative to each other in the first interference filter(s).

[0050] It is for example possible to have several first interference filters adapted to carry out filtering in the visible range, and one or more second interference filters adapted to carry out filtering in the infrared range. It is possible to produce at least one first interference filter adapted to carry out filtering in the visible range and at least one second interference filter adapted to carry out filtering in the infrared range, in which the volume proportions of the two materials with different refractive indices relative to each other are similar in the first and second interference filters, the spacer(s) alone present in the second filter making it possible to center the second filter on a wavelength different from that on which the first filter is centered.

[0051] The optical filtering device may comprise a total number of interference filters of between 5 and 15, or between 5 and 10. Such an optical filtering device may be integrated within a hyperspectral camera.

[0052] The interference filters of the optical filtering device may form an interference filter matrix.

[0053] Each semi-reflective layer may comprise at least one metallic material.

[0054] The invention also relates to an image sensor comprising at least one optical filtering device as defined previously, in which each of the first and second interference filters of the optical filtering device is arranged at one or more adjacent pixels of the image sensor.

[0055] The invention also relates to a method for producing an optical filtering device comprising at least first and second interference filters. each comprising at least one first Fabry-Perot cavity, comprising at least the following steps:

[0056] - production of a first semi-reflective layer of the first Fabry cavities- Perot;

[0057] - production, on the first semi-reflective layer, of a first layer structured comprising at least two materials of different refractive indices intended to be included in each of the first Fabry-Perot cavities, the first structured layer being common to the first and second interference filters and having a substantially constant thickness;

[0058] - production of at least one first spacer at the level of a region of the first structured layer intended to be part of the first Fabry-Perot cavity of the second interference filter;

[0059] - production of a second semi-reflective layer of the first Fabry cavities- Perot;

[0060] a distance between the first and second semi-reflective layers of the first Fabry-Perot cavity of the second interference filter being greater than a distance between the first and second semi-reflective layers of the first Fabry-Perot cavity of the first interference filter.

[0061] This method makes it possible to simultaneously produce several multilayer interference filters with Fabry-Perot cavities, for example arranged in a matrix, whose resonance wavelengths cover a spectral range not limited by the indices of the materials used. This method has the advantage of comprising few delicate steps, and the total number of steps implemented remains low. This method can comprise only two lithography steps, one of which is high definition (for producing the structured layer), to produce at least two filters whose spectral responses can be distributed in the complete visible and near infrared range. By simply modifying the mask used for the lithography of the layer to be structured, this method makes it possible to produce more filters positioned at intermediate wavelengths, for example more than 11 interference filters.

[0062] This method may include steps implemented in thin-film technology.

[0063] The production of the first structured layer may include the implementation of the following steps:

[0064] - deposition, on the first semi-reflective layer, of a layer of a first of the two materials with different refractive indices;

[0065] - lithography and etching of hollows in the layer of the first of the two materials of different refractive indices;

[0066] - deposition of a layer of a second of the two refractive index materials different in the hollows and on the layer of the first of the two materials of different refractive indices;

[0067] - planarization of the layer of the second of the two refractive index materials different with stopping on the layer of the first of the two materials with different refractive indices.

[0068] The production of the first spacer may include the implementation of the following steps:

[0069] - depositing an etching stop layer on the first structured layer;

[0070] - deposition, on the etching stop layer, of a layer of material intended to form the first spacer;

[0071] - lithography and etching of the layer of material intended to form the first spacer such that a remaining portion of said layer of material forms the first spacer.

[0072] The method may further comprise, prior to the production of the first semi-reflective layer, the production of second Fabry-Perot cavities superimposed on the first Fabry-Perot cavities.

[0073] In this case, the production of the second Fabry-Perot cavities may involve the implementation of the following steps:

[0074] - production, at the level of a first region of a substrate on which the first interference filter is intended to be produced, in a relief whose thickness is substantially equal to that of a second spacer of the second Fabry-Perot cavity of the second interference filter intended to be produced;

[0075] - depositing a third semi-reflective layer on the relief and on a second region of the substrate on which the second interference filter is intended to be produced;

[0076] - production of the second spacer on a part of the third semi-layer reflector intended to be part of the second Fabry-Perot cavity of the second interference filter;

[0077] - production, on the third semi-reflective layer, of a second layer structured comprising said at least two materials of different refractive indices intended to be included in each of the second Fabry-Perot cavities, the second structured layer being common to the first and second interference filters and having a substantially constant thickness;

[0078] and in which the first semi-reflective layer can then be produced on the second structured layer and also forms part of the second Fabry-Perot cavities. Brief description of the drawings

[0079] The present invention will be better understood upon reading the description of exemplary embodiments given purely for informational purposes and in no way limiting, with reference to the appended drawings in which:

[0080] - Figures 1 to 3 schematically represent an optical filtering device, object of the present invention, according to first, second and third embodiments;

[0081] - [Fig.4] represents the spectral responses of an optical filtering device, object of the present invention, according to the first particular embodiment;

[0082] - Figures 5 to 10 schematically represent steps of a method of production of an optical filtering device, object of the present invention, according to the first embodiment;

[0083] - [Fig.l 1] schematically represents an optical filtering device, the subject of the present invention, according to a fourth embodiment;

[0084] - [Fig. 12] represents the spectral responses of an optical filtering device, object of the present invention, according to the fourth embodiment;

[0085] - Figures 13 to 17 schematically represent steps of a method of production of an optical filtering device, object of the present invention, according to the fourth embodiment;

[0086] - [Fig. 18] schematically represents an image sensor, also the subject of the present invention, according to a particular embodiment.

[0087] Identical, similar or equivalent parts of the different figures described below bear the same numerical references so as to facilitate the transition from one figure to another.

[0088] The different parts represented in the figures are not necessarily on a uniform scale, in order to make the figures more readable.

[0089] The different possibilities (variants and embodiments) must be understood as not being mutually exclusive and can be combined with each other.

[0090] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0091] We first refer to [Fig.l] which represents an optical filtering device 100 according to a first embodiment.

[0092] The device 100 comprises a transparent substrate 102, comprising for example glass. A first antireflection layer 104 is arranged on the substrate 102. The first antireflection layer 104 comprises for example a dielectric material such as SiN. Its thickness is for example equal to approximately 50 nm, or more generally between approximately 10 nm and 70 nm. The value of the thickness of the layer 104 is a function of the spectral range targeted by the device 100 and of the refractive index. of the layer 104. Different values, and in particular greater than those indicated above, can be envisaged because the antireflection effect is periodic with the thickness of the layer 104. The layer 104 can be produced in the form of a thin layer. Several transparent layers at the desired wavelengths of the filters of the device 100, and of different refractive indices, can be arranged on the substrate 102, stacked on top of each other, such a multilayer being able to form a more efficient antireflection element than a single antireflection layer. Alternatively, the device 100 may not include an antireflection layer.

[0093] Interference filters 106 with Fabry-Perot cavities (six filters referenced 106.1 - 106.6 in [Fig.l]) are arranged on the first antireflection layer 104. The six filters 106.1 - 106.6 are such that the central wavelengths of the spectral responses of these filters are different from each other, and are respectively called Xiœ.i - Xi06.6- Generally, the device 100 may comprise at least two interference filters 106, and advantageously between 5 and 15 filters 106, or between 5 and 10 filters 106, or even an even greater number of filters 106. The number of filters 106 that the device 100 comprises depends on the number of distinct spectral responses desired in the spectral range to be processed by the device 100. Although in [Fig.l], the filters 106 are arranged next to each other along the y-axis, the filters 106 of the device 100 are generally arranged in the form of a filter matrix.

[0094] These filters 106 comprise a first semi-reflective layer 108, or semi-reflective mirror, which is here common to all the filters 106. The first semi-reflective layer 108 corresponds to a metallic layer, comprising for example silver and whose thickness is for example equal to approximately 44 nm or more generally between approximately 30 nm and 60 nm. The first anti-reflective layer 104 arranged between the substrate 102 and the first semi-reflective layer 108 makes it possible to avoid or limit light reflections on the first semi-reflective layer 108.

[0095] The filters 106 also comprise a structured layer 110 forming part of the middle of the filters 106 located between the semi-reflective layers of the filters 106. This structured layer 110 is common to all the filters 106 and of thickness eN which is substantially constant for all the filters 106. The structured layer 110 comprises at least two materials with different refractive indices nB and nH, here dielectric materials corresponding to SiN (index nH) and SiO2 (index nB), these two materials being structured such that the different regions of the structured layer 110 present in the different filters 106 comprise different volume proportions of these two materials so that the effective refractive index of the structured layer 110 varies from one filter to another. The material whose refractive index nH is the largest is called the first material, and here corresponds to SiN, and that whose refractive index nB is the smallest is called the second material, and here corresponds to SiO2. The materials of the structured layer 110 are transparent at least with respect to the wavelengths intended to be transmitted by the filters 106. Alternatively, at least one of the first and second materials may correspond to a semiconductor material.

[0096] In the example of [Fig. 1], a region 112.1 of the structured layer 110 forming part of the filter 106.1 comprises only the second material. A region 112.2 of the structured layer 110 forming part of the filter 106.2 comprises the first material in which hollows 114 are made throughout the thickness of the structured layer 110 and are filled with portions of the second material, thus forming structurings of the structured layer 110. In the example described here, these hollows 114, and therefore the portions of the second material, each have a section, in a main plane of the structured layer 110, that is to say a plane parallel to the face of the structured layer 110 lying against the first semi-reflective layer 108 (parallel to the plane (X,Y) in [Fig.l]), of rectangular or square shape. The period of the structuring is less than the value of the central wavelength of the spectral response of the 106.2 filter.The structures of the structured layer 110 may have shapes other than rectangular or square, for example groove or trench shapes made over the entire length or width of the filter. A region 112.3 of the structured layer 110 forming part of the filter 106.3 comprises only the first material. The filters 106.4, 106.5 and 106.6 each comprise a region 112.4, 112.5 and 112.6 of the structured layer 110 which are here similar to the regions 112.1, 112.2 and 112.3 respectively.

[0097] An etch stop layer 116 is disposed on the structured layer 110. This etching stop layer 116 comprises a material that etches much more slowly than the materials of the spacer 120 described later, for example AIN or TiO2, and which is transparent with respect to the wavelengths intended to be transmitted by the filters 106. The thickness of the etching stop layer 116 is for example between approximately 5 nm and 10 nm. This etching stop layer 116 is present in the filtering device 100 due to the production method implemented and which is described later in connection with FIGS. 5 to 10.

[0098] For the filters 106.1 to 106.3, the transparent materials located between the semi-reflective layers of these filters correspond to those of the regions 112.1 to 112.3 of the structured layer 110 and to that of the etching stop layer 116. Thus, at the level of these filters 106.1 to 106.3, a second semi-reflective layer 118 is arranged directly on the etching stop layer 116. Thus, the light incident on the filters 106.1 to 106.3 is reflected between the semi-reflective layers 108 and 118 in the structured layer 110 and the etch stop layer 116. The height, or thickness, of the Fabry-Perot cavities of the filters 106.1 to 106.3 formed between the two semi-reflective layers 108 and 118 is equal to the sum of the thickness eN of the structured layer 110 and the thickness of the etch stop layer 116.

[0099] For the filters 106.4 to 106.6, the second semi-reflective layer 118 is not arranged directly on the etch stop layer 116 but on a spacer 120 corresponding here to a portion of dielectric material of refractive index ns and thickness es, arranged between the etch stop layer 116 and the second semi-reflective layer 118. The height, or thickness, of the Fabry-Perot cavities of the filters 106.4 to 106.6 formed between the two semi-reflective layers 108 and 118 is therefore different from that of the filters 106.1 to 106.3 due to the presence of the spacer 120, thus modifying the values ​​of the central wavelengths X106.4 to Xi06.6 of the spectral responses of these filters with respect to those of the wavelengths central X106.1 to X106.3 of the spectral responses of filters 106.1 to 106.3.This thickness is equal to the sum of the thickness eN of the structured layer 110, the thickness of the etch stop layer 116 and the thickness es of the spacer 120. The material of the spacer 120 corresponds for example to one of the materials of the structured layer, advantageously that of the lowest index nB, or to any other dielectric or semiconducting material. The spacer 120 comprises a material transparent to the wavelengths intended to be transmitted by the filters 106.4 to 106.6. In the example of [Fig.l], the spacer 120 comprises SiO2. Light incident on filters 106.4 to 106.6 is reflected between semi-reflective layers 108 and 118 in structured layer 110, etch stop layer 116 and spacer 120.

[0100] Generally, the device 100 comprises at least one filter whose height, or thickness, is different from one or more other filters of the device 100 due to the presence of the spacer 120 in this filter.

[0101] A second anti-reflective layer 122 is arranged on the second semi-reflective layer 118 at the level of all the filters 106, and makes it possible to avoid or limit light reflections on the second semi-reflective layer 118. This second anti-reflective layer 122 is for example of a thickness similar to that of the layer 104. Several second anti-reflective layers 122 can be arranged on the second semi-reflective layer 118.

[0102] Thus, the values ​​of the central wavelengths of the spectral responses of the filters 106 of the device 100 are defined both by the value of the thickness of the Fabry-Perot cavities of the filters 106 which differ within the device 100, and by the value of the effective index of the medium between the semi-reflective layers which changes from one filter to another within the device 100 thanks to the structured layer 110.

[0103] The value of the thickness eN of the structured layer 110 is defined according to the equation (1) previously described (the stop layer 116 has little influence on the filtering carried out and, for the calculations carried out from the equation (1), it can be considered, as a first approximation, as absent from the filters 106). Thus, this thickness eN can be fixed by considering the characteristics of the first filter 106.1 whose wavelength Xi06.ia is the smallest value among those of the central wavelengths of the spectral responses of the filters 106 of the filtering device 100, that is to say as a function of the values ​​of Xioe.i and of the index nB of the second material which is the only one present in the region 112.1 of the structured layer 110 of the first filter 106.1. The value of the wavelength X106.3, i.e. the value of the largest central wavelength of the spectral responses among the filters which do not include the spacer 120, is a function of the thickness eN and the index nH of the first material which is the only one present in the region 112.3 of the structured layer 110 of the filter 106.3. For the filters which do not include the spacer 120 and which include regions of the structured layer 100 comprising structurings formed by the first and second materials (the filter 106.2 in the example of [Fig.l]), the dimensions of the structurings, corresponding to the dimensions of the hollows 114, can be calculated as described in the document US 2011 / 0290982 AL.

[0104] The value of the thickness es of the spacer 120 is fixed by considering the characteristics of the filter 106.4 whose wavelength X106.4 has the smallest value among those of the central wavelengths of the spectral responses of the filters which comprise the spacer 120, that is to say as a function of the values ​​of 7. m64 and of the index nB of the second material which is the only one present in the region 112.4 of the structured layer 110 of the filter 106.4, and also as a function of the refractive index ns of the material of the spacer 120.The equation (1) previously described can be used for the calculation of this thickness es, the numerator of this equation corresponding to the sum of the optical paths in each of the layers 110 and 120, i.e. 2nses + 2nBeN (as previously, for reasons of simplification of the calculations carried out from the equation (1), the etching stop layer 116 is considered, as a first approximation, as absent from the filters 106 due to the low impact of this layer on the filtering carried out). The value of the wavelength X106.6, that is to say the value of the largest central wavelength of the spectral responses among the filters which comprise the spacer 120, is a function of the thicknesses eN and es and of the index nH of the first material which is the only one present in the region 112.6 of the structured layer 110 of the filter 106.6 (the optical paths considered are paths. optical in each of the layers 110 and 120, i.e. 2nses + 2nHeN). For the filters which comprise the spacer 120 and which comprise regions of the structured layer 100 comprising structurings (the filter 106.5 in the example of [Fig.l]), the dimensions of the structurings can be calculated as described in the document US 2011 / 0290982 A1.

[0105] The design of the device 100 may be such that X106.3 = X106.4 so that the spectral ranges covered by the two groups of filters (first group of filters 106.1 -106.3 which do not include the spacer 120 and second group of filters 106.4 - 106.6 which include the spacer 120) are contiguous and result in a single spectral range covering a wide spectrum. However, this may not be the case.

[0106] The modifications of the spectral responses induced by the Fresnel reflection at the interface between the structured layer 110 and the spacer 120, and by the etch stop layer 116 in the cavities of the filters 106, are generally not significant, and can be minimized or optimized wisely by conventional methods of simulating multilayer stacks using software using multilayer optimization algorithms based on the Abélès formalism such as the needle method as described for example in the document “Application of the needle optimization technique to the design of optical coatings” and AV Tikhonravov et al., Applied Optics, vol. 35, no. 28, pages 5493-5508, October 1, 1996.

[0107] In the first embodiment previously described, the spacer 120 is arranged between the second semi-reflective layer 118 and the structured layer 110. Alternatively, the spacer 120 can be arranged between the first semi-reflective layer 108 and the structured layer 110, with in this case a relief previously formed on the substrate 102, as described later in connection with FIGS. 11 to 18.

[0108] The etch stop layer 116 is present at least at the level of the filters 106 which do not include the spacer 120. For reasons of simplification of implementation, the etch stop layer may be present at the level of all the filters 106, as is the case in the example of [Fig.l]. The etch stop layer 116 is arranged on or under the structured layer 110 depending on whether the spacer 120 is arranged on or under the structured layer 110.

[0109] The semi-reflective layers 108 and 118 preferably comprise at least one metal. The refractive index of a metal is complex and can be denoted n + zk. The metal forming the semi-reflective layers 108 and 118 is preferably chosen such that the ratio k / n is as high as possible, for example at least equal to approximately 10, throughout the spectral range covered by the interference filters 106 in order to obtain good transmission of wavelengths at order 1 and good rejection of wavelengths at higher orders, which is the case for silver.

[0110] Alternatively, the filters 106.4 to 106.6 may comprise several spacers 120 formed from one or more materials transparent to the wavelengths intended to be transmitted by the filters 106.4 - 106.6.

[0111] As a variant of the first embodiment, the device 100 may comprise, in addition to the filters 106.1 to 106.6, other filters formed from the semi-reflective layers 108 and 118, of the structured layer 110, but which comprise one or more spacers such that the height, or the thickness, of the Fabry-Perot cavities of these filters is different from those of the filters 106.1 to 106.6. The device 100 may comprise several groups of filters 106 each including one (or more) spacer of different thickness and / or of different material(s). It is in particular possible that all the groups of filters (each group of filters corresponding to the filters having the same thickness) comprise a spacer. The presence of a spacer in all of the filters 106 may improve adhesion when depositing the second semi-reflective layer 118 on these spacers, compared to depositing the second semi-reflective layer 118 directly on the etch stop layer 116.

[0112] In the first embodiment previously described, the hollows 114 are made through the entire thickness of the structured layer 110. In a second embodiment shown in [Fig. 2], the hollows 114 are made through a portion of the thickness of the structured layer 110. Thus, the first material of refractive index nH is also present under the portions of the second material of refractive index nB filling the hollows 114. The fact that the hollows 114 only pass through a portion of the thickness of the structured layer 110 implies that to obtain a given effective refractive index at a region of the structured layer 110 which comprises these hollows (corresponding to the regions 112.2 and 112.5 in [Fig.2]), the lateral dimensions of the hollows 114, that is to say the dimensions in the plane (X,Y), are greater than those of hollows making it possible to obtain this same effective refractive index but which would be produced throughout the thickness of the structured layer 110.

[0113] In the two embodiments previously described, in each group of filters 106, only one filter (the filter 106.2 for the group of filters not comprising the spacer 120, and the filter 106.5 for the group of filters comprising the spacer 120) comprises structurings. It is however possible that in each group of filters, several filters, or even all the filters, comprise structurings of different dimensions in order to obtain different spectral responses.

[0114] In the two embodiments previously described, the device 100 comprises a single structured layer 100 common to all the filters 106 and arranged between the semi-reflective layers 108 and 118 of these filters 106. [Fig. 3] represents the device 100 according to a third embodiment comprising ten filters 106.1 to 106.10, each of these filters comprising between the two semi-reflective layers 108 and 118, two parts of two structured layers 110.1 and 110.2 arranged one on top of the other. The filters 106.1 to 106.5 form the first group of filters not comprising the spacer 120, and the filters 106.6 to 106.10 form the second group of filters comprising the spacer 120.

[0115] Filter 106.1 includes regions 112.11 and 112.21 of the structured layers 110.1 and 110.2 comprising only the second material. The filter 106.2 comprises a region 112.12 of the first structured layer 110.1 comprising only the second material, and a region 112.22 of the second structured layer 110.2 comprising the first material in which depressions 114.2 are made through the entire thickness of the second structured layer 110.2 and are filled with the second material. The filter 106.3 comprises regions 112.13 and 112.23 of the structured layers 110.1 and 110.2 comprising the first material in which depressions 114.1 and 114.2 are made and filled with the second material. The filter 106.4 comprises a region 112.14 of the first structured layer 110.1 comprising only the first material, and a region 112.24 of the second structured layer 110.2 comprising the first material in which depressions 114.2 are made through the entire thickness of the second structured layer 110.2 and are filled with the second material.Finally, filter 106.5 has regions 112.15 and 112.25 of structured layers 110.1 and 110.2 comprising only the first material. Regions 112.16 to 112.20 and 112.26 to 112.30 of structured layers 110.1 and 110.2 in filters 106.6 to 106.10 are similar to those of filters 106.1 to 106.5.

[0116] Thus, the effective index in the regions of the structured layers 110.1 and 110.2 differ, in each group of filters, from one filter to another, which makes it possible to produce filters having different spectral responses. The combination of the regions of several superimposed structured layers therefore makes it possible to produce a greater number of regions with different effective refractive index, given that the accessible lateral dimensions of the structures are limited by the technological possibilities. In return, the method for producing the filtering device according to the third embodiment is more complex than for producing a filtering device comprising only a single structured layer as in the first and second embodiments.

[0117] As in the second embodiment, the hollows made in the structured layers 110.1 and 110.2 can be made through only a part of the thickness of these layers.

[0118] [Fig.4] represents spectral responses (i.e. the value of the transmission coefficient T as a function of the wavelength, in nanometers in [Fig.4]) obtained for a filtering device 100 comprising a single structured layer 110 in which the structuring is carried out throughout the thickness of the structured layer 110. This filtering device comprises six filters 106 not comprising the spacer 120 and whose spectral responses correspond to the curves referenced 10, 12, 14, 16, 18 and 20, and five filters comprising the spacer 120 and whose spectral responses correspond to the curves referenced 22, 24, 26, 28 and 30.

[0119] The filtering device 100 making it possible to obtain the spectral responses represented in [Fig.4] comprises the following elements:

[0120] - glass substrate 102;

[0121] - first anti-reflective layer 104 in SiN and with a thickness equal to 50 nm;

[0122] - first semi-reflective layer 108 in Ag and of thickness equal to 44 nm;

[0123] - structured layer 110 of thickness eN equal to 105 nm, the second material of which is SiO2, the first material of which is SiN and comprising structures, and therefore hollows 114, of rectangular shape;

[0124] - spacer 120 in SiO2 and thickness equal to 80 nm;

[0125] - second semi-reflective layer 118 in Ag and of thickness equal to 50 nm;

[0126] - second anti-reflective layer 122 in SiN and with a thickness equal to 42 nm.

[0127] The SiN used in this filtering device is enriched in silicon, which gives it a relatively high refractive index, close to that of TiO2, with in return a certain absorption of low wavelengths (which has no impact in the present case since the filters whose spectral response is in the blue contain little or no SiN).

[0128] At the filters comprising the spacer 120, the second antireflection layer 122 is covered with a portion of amorphous silicon with a thickness for example equal to 15 nm. This portion of amorphous silicon makes it possible, at the low wavelengths corresponding approximately to those of the blue color, to attenuate “rebounds” or secondary peaks of the spectral responses of the filters comprising the spacer 120 and whose central wavelengths are the largest. These rebounds are caused by the orders higher than order 1 of the Fabry-Perot cavities of these filters. The portion of amorphous silicon is transparent in the rest of the spectral domain. This portion of amorphous silicon also makes it possible, by constructive interference, to increase the transmission of the filters at which the portion of amorphous silicon is located.

[0129] The eleven filters of this filtering device cover a spectral band between approximately 450 nm and 900 nm. The central wavelengths of the spectral responses (of order 1) are uniformly distributed in this spectral band which covers the major part of the visible and near infrared spectrum. The six filters interference filters not comprising the spacer 120 and whose spectral responses correspond to the curves referenced 10, 12, 14, 16, 18 and 20 cover a first part of this spectral band ranging from approximately 450 nm to approximately 680 nm. The five interference filters comprising the spacer 120 and whose spectral responses correspond to the curves referenced 22, 24, 26, 28 and 30 cover a second part of this spectral band ranging from approximately 720 nm to approximately 900 nm.

[0130] The relative volume proportions of SiO2 and SiN in the regions of the structured layer 110 within these different filters are indicated in the table below. In this table, the filters are identified by the value of the central wavelength of their spectral response. The widths of the SiN pads in the regions of the structured layer 110, the widths of the spaces between these pads, as well as the period of these pads, are also indicated in this table. Central wavelength (nm) Relative proportion SiO2 / SiN (%) Thickness spacer (nm) Width of SiN plot (nm) Width of spaces between plots (nm) Period (nm) 450 100 / 0 0 0 0 0 500 85 / 15 0 135 215 350 540 70 / 30 0 195 155 350 580 50 / 50 0 250 100 350 630 30 / 70 0 290 60 350 680 0 / 100 0 0 0 0 720 85 / 15 80 135 215 350 750 70 / 30 80 195 155 350 800 50 / 50 80 250 100 350 840 30 / 70 80 290 60 350 900 0 / 100 80 0 0 0

[0131] Figures 5 to 10 represent steps of a method of producing the device 100 previously described in connection with [Fig.l].

[0132] The first antireflective layer 104 is first deposited on the substrate 102, then the first semi-reflective layer 108 is deposited on the first antireflective layer 104. A layer 124 comprising the first material and of thickness equal to the thickness eN of the structured layer 110 intended to be produced is then deposited on the first semi-reflective layer 108 ([Fig.5]). Advantageously, prior to the deposition of the layer 124, the first semi-reflective layer 108 can be encapsulated by a thin protective layer (not shown in the figures) to prevent degradation of the metal of the first semi-reflective layer 108 by air or by etching of the layer 124 carried out subsequently.

[0133] Steps of lithography and etching of the layer 124 are then implemented in order to form the hollows 114 at the regions of the structured layer intended to comprise structuring, and thus remove the parts of the layer 124 located at the regions of the structured layer 110 intended not to comprise the first material ([Fig.6]).

[0134] As shown in [Fig.7], a layer 126 comprising the second material and having a thickness at least equal to the thickness eN of the structured layer 110, and generally equal to two or three times the thickness eN to facilitate the implementation of the following polishing, is then deposited on the previously produced structure, in the etched parts of the layer 124 (i.e. in the recesses 114 and at the regions of the structured layer 110 intended to comprise only the second material). Parts of the layer 126 are also deposited on the remaining parts of the layer 124.

[0135] Chemical mechanical polishing (CMP) is then carried out with stopping on the remaining portions of layer 124, thus removing the parts of layer 126 deposited on the remaining parts of layer 124 ([Fig.8]), and forming the structured layer 110.

[0136] As shown in [Fig.9], the etch stop layer 116 is then deposited on the structured layer 110, then a layer 127 comprising the material of the spacer 120 and of thickness es is deposited on the etch stop layer 116.

[0137] Steps of lithography and etching of the layer 127 are then implemented so that a remaining portion of the layer 127 forms the spacer 120 ([Fig. 10]). The presence of the etching stop layer 116 at the level of the etched portion(s) of the layer 127 prevents over-etching in the structured layer 110 during the etching of the layer 127.

[0138] The second semi-reflective layer 118 is then deposited on the entire structure, i.e. on the spacer 120 and on the part or parts of the etch stop layer 116 not covered by the spacer 120. A thin adhesion layer (not shown) can be deposited on the entire structure, prior to the deposition of the second semi-reflective layer 118. The second anti-reflective layer 122 is then deposited on the second semi-reflective layer 118. The device obtained corresponds to the device 100 shown in [Fig.l].

[0139] [Fig. 11] represents the filtering device 100 according to a fourth embodiment in which each interference filter 106.1 - 106.6 comprises two Fabry-Perot cavities superimposed one above the other.

[0140] The device 100 comprises the first antireflection layer 104 arranged on the substrate 102. The thickness of the part of the first antireflection layer 104 formed at the first group of filters 106.1 - 106.3 not comprising a spacer is greater than that of the part of the first antireflection layer 104 formed at the second group of filters 106.4 - 106.6. A third semi-reflective layer 128 is arranged on the first anti-reflective layer 104. At the level of the second group of filters 106.4 - 106.6, a second spacer 120.2 is produced on the third semi-reflective layer 128. The first anti-reflective layer 104 thus forms, at the level of a first region of the substrate 102 on which the first group of filters 106.1 - 106.3 is intended to be produced, a relief whose thickness is substantially equal to that of the second spacer 120.2.The sum of the thicknesses of the third semi-reflective layer 128 and of the part of the first anti-reflective layer 104 at the level of the first group of filters 106.1 - 106.3 is therefore substantially equal to that of the thicknesses of the second spacer 120.2, of the third semi-reflective layer 128 and of the part of the first anti-reflective layer 104 at the level of the second group of filters 106.4 - 106.6. Alternatively, this relief could be produced by hollowing out the substrate 102, the first anti-reflective layer 104 being able in this case to have a constant thickness.

[0141] An upper face of the third semi-reflective layer 128 at the level of the first group of filters 106.1 - 106.3 and an upper face of the second spacer 120.2 form a flat surface on which is arranged a second etching stop layer 116.2 whose role is to protect the second spacer 120.2.

[0142] The device 100 comprises a second structured layer 110.2 common to all the filters 106.1 - 106.6. The second structured layer 110.2 comprises the two materials with different refractive indices and, in certain regions, structures similar to those previously described in connection with [Fig.l]. The second structured layer 110.2 is here similar to the structured layer 110 previously described in connection with [Fig.l].

[0143] The first semi-reflective layer 108, comprising for example a material similar to that of the third semi-reflective layer 128, is arranged on the second structured layer 110.2. Thus, for each of the filters 106.1 - 106.6, a second Fabry-Perot cavity is formed between the two semi-reflective layers 108 and 128. First Fabry-Perot cavities, similar to those of the device 100 previously described in connection with [Fig.l], are then produced on the second Fabry-Perot cavities.

[0144] The first structured layer 110.1 common to all filters 106.1 - 106.6 is disposed on the first semi-reflective layer 108. The first structured layer 110.1 is similar to the second structured layer 110.2.

[0145] The first etch stop layer 116.1 is arranged on the first structured layer 110.1.

[0146] The first spacer 120.1, for example similar to the second spacer 120.2, is arranged on the first etch stop layer 116.1 at the second filter group 106.4 - 106.6. The second semi-reflective layer 118 is arranged on the first spacer 120.1 and, at the first filter group 106.1 - 106.3, on the first etch stop layer 116.2.

[0147] The second anti-reflective layer 122, for example similar to that previously described in connection with [Fig.l], is arranged on the second semi-reflective layer 118. At the level of each of the filters 106.1 - 106.6, the two Fabry-Perot cavities formed may be similar to each other.

[0148] Compared to the interference filters of the device 100 according to the first embodiment, those of the device 100 according to the fourth embodiment have better rejection and better selectivity.

[0149] Because the production of each of the structured layers 110.1 and 110.2 requires the implementation of a planarization step, for example by CMP, each structured layer 110.1 and 110.2 is produced on a flat face (the upper face of the second etch stop layer 116.2 for the second structured layer 110.2 and the upper face of the first semi-reflective layer 108 for the first structured layer 110.1). For this, the second spacer 120.2 is arranged under the second structured layer 110.2. Thus, after the production of the second Fabry-Perot cavities of the filters 106.1 - 106.6, the surface on which the first Fabry-Perot cavities of the filters 106.1 - 106.6 are produced is flat.

[0150] [Fig. 12] represents the spectral responses obtained for a filtering device similar to that described in connection with [Fig.l 1], that is to say comprising two structured layers 110.1 and 110.2 in which the structuring is carried out through the entire thickness and forming, for each filter, two Fabry-Perot cavities superimposed one above the other. This filtering device comprises six interference filters not comprising the spacers 120.1 and 120.2 and whose spectral responses correspond to the curves referenced 40, 42, 44, 46, 48 and 50, and five interference filters comprising the spacers 120.1 and 120.2 and whose spectral responses correspond to the curves referenced 52, 54, 56, 58 and 60.

[0151] The filtering device 100 making it possible to obtain the spectral responses represented in [Fig. 12] comprises the following elements:

[0152] - glass substrate 102;

[0153] - first antireflective layer 104 in SiN and of thickness equal to 20 nm at the level of the five filters comprising the spacers, and of thickness equal to 100 nm at the level of the six filters not comprising the spacers;

[0154] - third semi-reflective layer 128 in Ag and of thickness equal to 27 nm;

[0155] - second spacer 120.2 in SiO2 and of thickness equal to 80 nm;

[0156] - second structured layer 110.2 of thickness eN equal to 105 nm, the second material of which is SiO2, the first material of which is SiN and comprising rectangular-shaped hollows 114;

[0157] - first semi-reflective layer 108 in Ag and of thickness equal to 61 nm;

[0158] - first structured layer 110.1 of thickness eN equal to 105 nm, the second material of which is SiO2, the first material of which is SiN and comprising rectangular-shaped hollows 114;

[0159] - first spacer 120.1 in SiO2 and of thickness equal to 80 nm;

[0160] - second semi-reflective layer 118 in Ag and of thickness equal to 27 nm;

[0161] - second anti-reflective layer 122 in SiN and with a thickness equal to 67 nm.

[0162] As in the previously described embodiment, the SiN used in this filtering device is enriched in silicon and, at the level of the filters comprising the spacers 120.1 and 120.2, the second antireflection layer 122 is covered with a portion of amorphous silicon with a thickness equal to 120 nm.

[0163] The eleven filters of this filtering device cover a spectral band between approximately 450 nm and 900 nm. The central wavelengths of the spectral responses (of order 1) are uniformly distributed in this spectral band which covers the major part of the visible and near infrared spectrum. The six interference filters not comprising the spacers 120.1 and 120.2 and whose spectral responses correspond to the curves referenced 40, 42, 44, 46, 48 and 50 cover a first part of this spectral band ranging from approximately 450 nm to approximately 680 nm. The five interference filters comprising the spacers 120.1 and 120.2 and whose spectral responses correspond to the curves referenced 52, 54, 56, 58 and 60 cover a second part of this spectral band ranging from approximately 720 nm to approximately 900 nm. Compared to the spectral responses represented in [Fig. 4], those represented in [Fig.12] present maximum amplitudes more homogeneous with respect to each other, thanks to the superposition of two Fabry-Perot cavities in each of the filters 106. .

[0164] Figures 13 to 17 represent steps of a method of producing the filtering device 100 previously described in connection with [Fig.l 1].

[0165] A first layer 130, from which the first antireflection layer 104 is intended to be produced, is deposited on the substrate 102 ([Fig. 13]). The thickness of this first layer 130 is equal to the thickness of the second spacer 120.2 intended to be produced.

[0166] As shown in [Fig. 14], lithography and etching of this first layer 130 are then implemented in the first layer 130 such that a remaining portion 132 of the first layer 130 is intended to form a part of the first antireflection layer 104 located at the level of the filters 106.1 - 106.3 not comprising spacers.

[0167] The first antireflection layer 104 is then completed by depositing a material similar to that of the first layer 130 both on the remaining portion 132 of the first layer 130 and on the part of the substrate 102 not covered by the remaining portion 132, with a thickness equal to that of the part of the first antireflection layer 104 intended to be located at the filters intended to comprise the spacers 120.1 and 120.2.

[0168] The third semi-reflective layer 128 is then deposited on the first anti-reflective layer 104. A layer intended to form the second spacer 120.2, i.e. comprising the material of this second spacer 120.2 and whose thickness is at least equal to that of the second spacer 120.2 is then deposited on the third semi-reflective layer 128. A CMP type planarization is then implemented with a stop on the part of the third semi-reflective layer 128 (or of a thin protective layer not shown) located on the part of the first anti-reflective layer 104 whose thickness is the greatest. The remaining portion of this layer forms the second spacer 120.2 ([Fig. 15]).

[0169] As shown in [Fig. 16], the second etch stop layer 116.2 is then deposited on the previously produced structure, i.e. on the second spacer 120.2 and on the part of the third semi-reflective layer 128 located on the part of the first anti-reflective layer 104 whose thickness is the greatest.

[0170] A layer 134 comprising the first material and of thickness equal to the thickness eN of the second structured layer 110.2 intended to be produced is then deposited on the second etching stop layer 116.2.

[0171] Steps of lithography and etching of the layer 134 are then implemented in order to form the hollows 114, that is to say to remove the parts of the layer 134 located at the regions of the second structured layer 110.2 intended not to comprise the first material. A layer comprising the second material and of thickness at least equal to the thickness eN of the second structured layer 110.2 is then deposited on the previously produced structure, in the etched parts of layer 134 (i.e. in the recesses 114 and at the regions of the second structured layer 110.2 intended to comprise only the second material). Portions of this layer are also deposited on the remaining portions of layer 134.

[0172] Chemical mechanical polishing (CMP) is then performed with stopping on the remaining portions of the layer 134, thus removing the parts of the layer deposited on the remaining parts of the layer 134 and forming the second structured layer 110.2 ([Fig. 17]).

[0173] The first semi-reflective layer 108 is then deposited on the second structured layer 110.2, then the first structured layer 110.1 is then produced by implementing steps similar to those producing the second structured layer 110.2. The device 100 is then completed by implementing steps similar to those previously described in connection for producing the device 100 according to the first embodiment.

[0174] In the previously described embodiments, the materials of the structured layers 110, 110.1 and 110.2 and of the spacers 120, 120.1 and 120.2 are dielectric materials. Alternatively, one or more of these materials may be semiconductor materials, for example amorphous or polycrystalline silicon, ZnO, ZnS, ZnSe, or ZnTe.

[0175] [Fig. 18] schematically represents an image sensor 1000 according to a particular embodiment.

[0176] The image sensor 1000 comprises an electronic part 1002, formed for example of CMOS type detection elements forming pixels 1004. The filtering device 100 is integrated on the front face of this electronic part 1002, such that the filters 106 are arranged opposite the pixels 1004. It is possible for each filter 106 to be arranged opposite a pixel 1004, or opposite several adjacent pixels. The image sensor 1000 may correspond to a hyperspectral camera, and may comprise other elements, for example optical and electronic such as electrical interconnections and micro-lenses, not shown in [Fig. 18].

Claims

1. Claims Optical filtering device (100) comprising at least first and second interference filters (106.1 - 106.10) each comprising at least one first Fabry-Perot cavity formed by first (108) and second (118) semi-reflective layers between which at least one first structured layer (110.1) is arranged, in which: - the first structured layer (110.1) is common to the first and second interference filters (106.1 - 106.10), has a substantially constant thickness and comprises first portions of at least two materials, dielectric or semi-conductor, of different refractive indices arranged, in each of the first Fabry-Perot cavities and in a plane parallel to the first semi-reflective layer (108), one next to the other in an alternating manner; - the first Fabry-Perot cavity of the second interference filter (106.4 - 106.6; 106.6 - 106.10) comprises at least one first spacer (120, 120.1) arranged between one of the first (108) and second (118) semi-reflective layers and the first structured layer (110.1) such that a distance between the first (108) and second (118) semi-reflective layers of the first Fabry-Perot cavity of the second interference filter (106.4 - 106.6; 106.6 - 106.10) is greater than a distance between the first (108) and second (118) semi-reflective layers of the first Fabry-Perot cavity of the first interference filter (106.1 - 106.3; 106.1 -106.5); and wherein the first and second interference filters (106.1 - 106.10) are produced according to a first configuration and / or a second configuration such that: - according to the first configuration, the device (100) further comprises a second structured layer (110.2) arranged between the first (108) and second (118) semi-reflective layers, common to the first and second interference filters (106.1 -106.10), having a substantially constant thickness and comprising second portions of the two materials of different refractive indices arranged, in each of the first Fabry-Perot cavities and in the plane parallel to the first semi-reflective layer (108), one next to the other in an alternating manner; - according to the second configuration, the first and second interference filters (106.1 - 106.10) each comprise at least one second Fabry-Perot cavity superimposed on the first Fabry-Perot cavity and formed by the first (108) and a third (128) semi-reflective layers between which at least one second structured layer (110.2) is arranged, the second structured layer (110.2) being common to the first and second interference filters (106.1 - 106.10), having a substantially constant thickness and comprising second portions of the two materials of different refractive indices arranged, in each of the second Fabry-Perot cavities and in the plane parallel to the first semi-reflective layer (108), one next to the other in an alternating manner, the second Fabry-Perot cavity of the second interference filter (106.4 - 106.6; 106.6 - 106.10) further comprising at least one second spacer (120.2) arranged between the third semi-reflective layer (128) and the second structured layer (110.2) such that a distance between the first (108) and third (128) semi-reflective layers of the second Fabry-Perot cavity of the second interference filter (106.4 - 106.6; 106.6 - 106.10) is greater than a distance between the first (108) and third (128) semi-reflective layers of the second Fabry-Perot cavity of the first interference filter (106.1 -106.3; 106.1- 106.5).

2. Optical filtering device (100) according to claim 1, wherein the first structured layer (110.1) and / or the second structured layer (110.2) comprise periodic patterns formed respectively by the first and / or second portions of a second of the two materials of different refractive indices arranged in a layer (124) of a first of the two materials of different refractive indices formed respectively of the first and / or second portions of the first of the two materials of different refractive indices.

3. An optical filtering device (100) according to claim 2, wherein, in each of the first and / or second Fabry-Perot cavities, values of dimensions and a period of the periodic patterns are less than a value of a central wavelength of a spectral response respectively of said first and / or second Fabry-Perot cavity at order 1.

4. Optical filtering device (100) according to one of claims 2 or 3, wherein the first and / or second portions of the second of the two materials with different refractive indices are formed throughout the thickness of the first structured layer (110.1) and / or the second structured layer (110.2) respectively.

5. Optical filtering device (100) according to one of the preceding claims, further comprising at least one first etch stop layer (116) arranged at least between one of the first (108) and second (118) semi-reflective layers and the first structured layer (110, 110.1) in the first Fabry-Perot cavity of the first interference filter (106.1 - 106.3; 106.1 -106.5).

6. Optical filtering device (100) according to one of the preceding claims, wherein the first spacer (120, 120.1) and the first etch stop layer (116.1) are arranged between the first structured layer (110, 110.1) and the second semi-reflective layer (118), and wherein, according to the second configuration, a second etch stop layer (116.2) is arranged between the second structured layer (110.2) and the third semi-reflective layer (128).

7. Optical filtering device (100) according to one of the preceding claims, further comprising at least one portion of material absorbing with respect to wavelengths of values lower than that of a central wavelength of a spectral response of the first Fabry-Perot cavity of the second interference filter (106.4 - 106.6; 106.6 - 106.10), arranged on or in the first Fabry-Perot cavity of the second interference filter (106.4 - 106.6; 106.6 -106.10).

8. Optical filter device (100) according to one of the preceding claims, comprising several first interference filters (106.1- 106.3; 106.1 - 106.5) arranged next to each other and in which volume proportions of the two materials with different refractive indices relative to each other in the first structured layer (110, 110.1) and / or the second structured layer (110.2) are different from one first interference filter to the other, and / or comprising several second interference filters (106.4 - 106.6; 106.6 - 106.10) arranged next to each other and in which volume proportions of the two materials with different refractive indices relative to each other in the first structured layer (110, 110.1) and / or the second structured layer (110.2) are different from one second interference filter to the other.

9. An image sensor (1000) comprising at least one optical filtering device (100) according to one of the preceding claims, wherein each of the first and second interference filters (106.1 - 106.10) of the optical filtering device (100) is arranged at one or more adjacent pixels (1004) of the image sensor (1000).

10. Method for producing an optical filtering device (100) comprising at least first and second interference filters (106.1 - 106.10) each comprising at least one first Fabry-Perot cavity, comprising at least the following steps: - producing a first semi-reflective layer (108) of the first Fabry-Perot cavities; - producing, on the first semi-reflective layer (108), a first structured layer (110.1) common to the first and second interference filters (106.1 - 106.10), having a substantially constant thickness and comprising first portions of at least two materials, dielectric or semi-conductor, of different refractive indices intended to be arranged, in each of the first Fabry-Perot cavities and in a plane parallel to the first semi-reflective layer (108), one next to the other in an alternating manner; - production of at least one first spacer (120, 120.1) at a region of the first structured layer (110.1) intended to be part of the first Fabry-Perot cavity of the second interference filter (106.4- 106.6; 106.6- 106.10); - production of a second semi-reflective layer (118) of the first Fabry-Perot cavities; a distance between the first (108) and second (118) semi-reflective layers of the first Fabry-Perot cavity of the second interference filter (106.4 - 106.6; 106.6 - 106.10) being greater than a distance between the first (108) and second (118) semi-reflective layers of the. first Fabry-Perot cavity of the first interference filter (106.1 -106.3; 106.1- 106.5), and wherein the first and second interference filters (106.1 - 106.10) are produced according to a first configuration and / or a second configuration such that: - according to the first configuration, the method further comprises, between the production of the first structured layer (110.1) and the production of the first spacer (120, 120.1), the production of a second structured layer (110.2) intended to be arranged between the first (108) and second (118) semi-reflective layers, common to the first and second interference filters (106.1-106.10), having a substantially constant thickness and comprising second portions of the two materials of different refractive indices arranged, in each of the first Fabry-Perot cavities and in the plane parallel to the first semi-reflective layer (108), one next to the other in an alternating manner; - according to the second configuration, the method further comprises, before the production of the first semi-reflective layer (108), the production of at least one second Fabry-Perot cavity of each of the first and second interference filters (106.1 -106.10), superimposed on the first Fabry-Perot cavity and formed by the first (108) and a third (128) semi-reflective layers between which at least one second structured layer (110.2) is produced, the second structured layer (110.2) being common to the first and second interference filters (106.1 - 106.10), having a substantially constant thickness and comprising second portions of the two materials of different refractive indices arranged, in each of the second Fabry-Perot cavities and in the plane parallel to the first semi-reflective layer (108), one next to the other in an alternating manner, the second Fabry-Perot cavity of the second filter interferential (106.4 - 106.6; 106.6 - 106.10) further comprising at least one second spacer (120.2) arranged between the third semi-reflective layer (128) and the second structured layer (110.2) such that a distance between the first (108) and third (128) semi-reflective layers of the second Fabry-Perot cavity of the second interference filter (106.4 - 106.6; 106.6 - 106.10) is greater than a distance between the first (108) and third (128) semi-reflective layers of the second cavity. Fabry-Perot of the first interference filter (106.1 - 106.3; 106.1 -106.5).

11. The method of claim 10, wherein providing the first structured layer (110.1) comprises the implementation of the following steps: - deposition, on the first semi-reflective layer (108), of a layer (124) of a first of the two materials with different refractive indices; - lithography and etching of hollows (114) in the layer (124) of the first of the two materials with different refractive indices, forming the first portions of the first of the two materials with different refractive indices; - deposition of a layer (126) of a second of the two materials with different refractive indices in the hollows (114) and on the layer (124) of the first of the two materials with different refractive indices; - planarization of the layer (126) of the second of the two materials with different refractive indices with stopping on the layer (124) of the first of the two materials with different refractive indices, forming the first portions of the second of the two materials with different refractive indices.

12. Method according to one of claims 10 or 11, in which the production of the first spacer (120, 120.1) comprises the implementation of the following steps: - deposition of a first etch stop layer (116.1) on the first structured layer (110.1) or, when the first and second interference filters (106.1 - 106.10) are produced according to the first configuration, on the second structured layer (110.2); - deposition, on the first etch stop layer (116.1), of a layer (127) of material intended to form the first spacer (120, 120.1); - lithography and etching of the layer (127) of material intended to form the first spacer (120, 120.1) such that a remaining portion of said layer (127) of material forms the first spacer (120, 120.1).

13. A method according to one of claims 10 to 12, wherein, when the first and second interference filters (106.1 - 106.10) are produced according to the second configuration, the production of the second Fabry-Perot cavities comprises the implementation of the following steps: - production, at the level of a first region of a substrate (102) on which the first interference filter (106.1 - 106.3; 106.1 -106.5) is intended to be produced, of a relief whose thickness is substantially equal to that of the second spacer (120.2) intended to be produced; - depositing the third semi-reflective layer (128) on the relief and on a second region of the substrate (102) on which the second interference filter (106.4 - 106.6; 106.6 - 106.10) is intended to be realized; - production of the second spacer (120.2) on a part of the third semi-reflective layer (128) intended to be part of the second Fabry-Perot cavity of the second interference filter (106.4 - 106.6; 106.6 - 106.10), the second spacer (120.2) and a part of the third semi-reflective layer (128) intended to be part of the second Fabry-Perot cavity of the first interference filter (106.1 - 106.3; 106.1 - 106.5) forming a flat upper surface; - production, on said flat upper surface, of the second structured layer (110.2); and wherein the first semi-reflective layer (108) is then formed on the second structured layer (110.2).

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