Method for producing a multispectral filter array having curved fabry-perot filters

Abstract

The invention relates to a method (100) for producing a multispectral filter array for an electromagnetic wave, the method comprising the following steps: - depositing (101) a layer of structuring material on a substrate; - structuring (102) the layer of structuring material in order to obtain a first structuring material pattern and a second structuring material pattern, each resin pattern having a curved upper surface; - conformally depositing (103) a first reflective layer on the first and second patterns, forming the first reflective layers of a first and a second color filter; - depositing (104) a layer of dielectric material on the first reflective layer so as to form the curved lower surfaces of the Fabry-Perot cavity dielectric layers of the first and second filters; - structuring (105, 106) the layer of dielectric material by nanoimprint lithography by means of a printing mould comprising at least two different curved imprints so as to form the curved upper surfaces of the Fabry-Perot cavity dielectric layers; - conformally depositing (107) a second reflective layer on the layer of dielectric material.

Description

Description Title of the invention: Method for manufacturing a multispectral filtering matrix with curved Fabry-Pérot filters TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of spectral filtering, in particular for imaging applications and the production of color filters, infrared filters or other filters of longer wavelengths depending on the appropriate metal and cavity material, for CMOS type image sensors, liquid crystal display devices or light-emitting diodes. The invention can also be implemented in light-emitting devices.

[0002] The present invention relates to a method of manufacturing a multispectral filtering matrix. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] A spectral filter or a color filter allows light to be filtered by wavelength, in order to provide information on the intensity of light in certain wavelengths. Several color filters can be combined to form, for example, red-green-blue (RGB) filters which provide information on the intensity of these three colors.

[0004] In particular, metal / dielectric color filters are known, made from a Fabry-Pérot cavity. These filters comprise one or more dielectric (or possibly semiconductor) cavities formed between two thin metal films having a metal mirror function so as to form a Fabry-Pérot cavity. An example of this type of filter is described in document US6031653. Generally, the metal / dielectric stacks are different depending on the position on the optoelectronic component (an image sensor for example). The transmission of the filter is adjusted by adjusting the thickness of the cavity. Thus, in operation, a portion of the incident light corresponding to the wavelength of the filter is transmitted through it in the form of a colored beam, while the rest of the incident light is reflected.Generally speaking, the thickness of the dielectric layer determines the central transmitted wavelength, while the thickness of the metal layers allows the transmission spectral width to be adjusted. Furthermore, the use of several Fabry-Pérot cavities allows the spectral profile of the filter's transmission to be modified. A filter of this type is produced using conventional semiconductor manufacturing techniques. Thus, to obtain a red-green-blue filter, it is necessary to form at least one dielectric cavity whose thickness must have three different values.

[0005] However, even though wavelength selectivity can be achieved by varying the cavity thickness, a Fabry-Pérot cavity filter is also very sensitive to the angle of incidence. [Fig.l] shows the spectral response of a color filter to an electromagnetic wave, for a fixed dielectric layer thickness and different angles of incidence of the electromagnetic wave.

[0006] Many studies have been conducted to address this deficiency in the sensitivity of filters to the angle of incidence of electromagnetic waves. One way to reduce sensitivity, described in the following article: "Non-iridescent Transmissive Structural Color Filter Featuring Highly Efficient Transmission and High Excitation Purity. Sci Rep 4, 4921 (2014)", Shrestha, V., Lee, SS., Kim, ES. et al., is to use multiple cavities with a higher index cavity material. The authors of the article used the fact that the angle-dependent fractional wavelength shift is determined by the refractive index of the cavity: where 0 is the angle electromagnetic field of incidence and n is the refractive index of the cavity. The proposed solutions reduce angle sensitivity, but they require several lithography and etching steps for their fabrication.

[0007] Another way to reduce angular sensitivity is proposed in document US4466699A or in document KR101533202 which describe a Fabry-Pérot filter with two plates of curved surfaces or, more particularly, aspherical surfaces which are movable relative to each other along an axis. The curved surfaces make it possible to have an angle of incidence of the radiation which is not perpendicular to the surface at any point on the surface. The curvature of the plates is chosen such that the error introduced by the fact that the angle of incidence is not perpendicular is compensated by the difference in distance between the plates, to obtain the desired wavelength at the output of the filter.

[0008] However, the Fabry-Pérot filter proposed in these documents allows the spacing between the plates to be varied to obtain one wavelength at a time and not several wavelengths at a time. In addition, since the filter has a variable distance between the plates, it cannot be used in imaging, and in particular at microelectronics dimensions with CMOS image sensors, due to manufacturing constraints. Summary of the invention

[0009] The invention offers a solution to the problems mentioned above, by proposing a method for manufacturing a matrix comprising Fabry-Pérot filters making it possible to obtain several wavelengths, which is not very sensitive to the variation in the angle of incidence of electromagnetic radiation and can be used in CMOS technology, said method being moreover economical and simplified by making it possible to avoid dif- different stages of selective etching and / or selective deposition. [OO1O] To do this, the subject of the invention is a method for manufacturing a multispectral filtering matrix for an electromagnetic wave, the matrix comprising at least a first and a second color filter, each color filter forming a Fabry-Pérot cavity comprising a first reflective layer, a second reflective layer and a layer of Fabry-Pérot cavity dielectric material between the first reflective layer and the second reflective layer, the layer of dielectric material comprising: • a lower surface in contact with the first reflective layer, the lower surface being curved; • an upper surface in contact with the second reflective layer, the upper surface being curved; the thicknesses of the two layers of dielectric material of the two color filters being different, said method being implemented by means of at least one printing mold and comprising the following steps: • Deposition on a substrate of a layer of structuring material; • Structuring the layer of structuring material, to obtain a first pattern of structuring material and a second pattern of structuring material, each pattern having a curved upper surface; • Conformal deposition of a first reflective layer on the first and second patterns, forming the first reflective layers of the first and second color filters; • Deposition of a layer of dielectric material on the first reflective layer, the lower surface of the dielectric layer covering the curved upper surfaces of the first and second patterns coated with the first reflective layer so as to form the curved lower surfaces of the layers of Fabry-Pérot cavity dielectric material of the first and second filters; • Structuring of the dielectric material layer by nanoimprint lithography using the printing mold comprising at least two different curved imprints configured to form the curved upper surfaces of the Fabry-Pérot cavity dielectric material layers of the first and second filters so as to obtain different thicknesses of the two dielectric material layers; • Conformal deposition of a second reflective layer on the layer of dielectric material forming the second reflective layers of the first and second color filters.

[0011] Thanks to the device obtained via the method according to the invention, the transmission of the filters of colors is independent of the angle of incidence of an incident electromagnetic wave, which makes it possible to obtain a desired wavelength for each filter only by varying the thicknesses of the dielectric layers without worrying about the angles of incidence. In addition, the matrix includes Fabry-Pérot cavity filters used for imaging in microelectronics, and in particular in CMOS technologies.

[0012] The method according to the invention also considerably limits the successive selective deposition and selective etching steps for the production of each of the curved filters having different thicknesses thanks to the use of the nanoimprint mold; the latter also makes it possible to reduce the manufacturing costs of the matrix since the mold can be reused several times.

[0013] In addition to the characteristics which have just been mentioned in the preceding paragraph, the method according to the invention may have one or more additional characteristics among the following, considered individually or according to all technically possible combinations: • the printing mold is produced by Grayscale grayscale lithography; • the production of the printing mold involves the following steps: • Fabrication by grayscale lithography of a master structure comprising at least two convex curved patterns; • spreading a resin on the master structure so that the resin is structured by the patterns of the master structure; • depositing a layer of flexible film in contact with the structured resin; • crosslinking of the structured resin; • peeling off the flexible film layer on which the structured resin is attached in order to obtain the printing mold. • the mold impressions are concave impressions having a surface substantially in the shape of a portion of a sphere. • the step of structuring the layer of structuring material, to obtain a first pattern of structuring material and a second pattern of structuring material is carried out by nano-imprint lithography using a second mold comprising at least two identical curved imprints configured so as to obtain an identical shape for the upper surfaces of the first and second patterns. • the at least two cavities of the first mold have a surface substantially in the form of a portion of a sphere of identical radius and the at least two cavities of the second mold have a surface substantially in shape of a portion of a sphere of different radius. • the volume of the dielectric material of the dielectric material layer is determined by the difference between the sum of the volumes of the cavities of the first mold and the sum of the volumes of the cavities of the second mold. • According to another embodiment, the step of structuring the layer of structuring material, to obtain a first pattern of structuring material and a second pattern of structuring material is carried out by Grayscale grayscale lithography. • each color filter is formed opposite a photoelectric transducer.

[0014] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0015] The figures are presented for information purposes only and in no way limit the invention.

[0016] [Fig.l] is a representation of the spectral response of a state-of-the-art Fabry-Pérot cavity filter, as a function of the angle of incidence of an incident electromagnetic wave.

[0017] [Fig.2] is a diagram of a matrix obtained by the method according to the invention, comprising three different color filters respectively.

[0018] [Fig.3] shows the spectral response of a first color filter, for different angles of incidence of an electromagnetic wave incident on the first filter of [Fig.2],

[0019] [Fig.4] shows the spectral response of a second color filter, different from the first filter, for different angles of incidence of an electromagnetic wave incident on the second filter of [Fig.2].

[0020] [Fig.5] is a diagram illustrating the principle of decomposition into two structures at the basis of the method according to the invention.

[0021] [Fig.6] and [Fig.7] schematically illustrate the steps for producing the nano-imprint molds used in the process according to the invention.

[0022] [Fig.8] illustrates the steps of the method of one embodiment of the method according to the invention.

[0023] [Fig.9] is an illustration of a pixel matrix obtained by the method according to the invention. DETAILED DESCRIPTION

[0024] The figures are presented for information purposes only and in no way limit the invention.

[0025] It should be recalled first of all that, generally and well known to those skilled in the art, a metal / dielectric type color filter made from a Fabry-Pérot cavity is obtained by sizing the thickness of the dielectric layer formed between the two metal layers. If the filtering of several colors is sought on the same component, it is then necessary to be able to obtain a dielectric thickness of variable thickness on this same component.

[0026] This dimensioning is for example carried out using an electromagnetic calculation program such as the Abeles matrix transfer formalism or a diffraction calculation for pixels whose size is close to the wavelength such as the Fourier Expansion Modal Method formalism or rigorous coupled wave analysis (RCWA according to English terminology).

[0027] These calculation programs allow the optimal parameters of metal-dielectric stacks to be determined for each pixel. The calculation takes into account, in particular, the thicknesses of the metal and dielectric layers as well as their indices, the spectrum and the angular distribution of the incident light. For example, in the case of Fabry-Pérot filters, the central wavelength of the filter is determined approximately by the following formula: • h is the thickness of the cavity, i.e. approximately the thickness of the dielectric layer • m, a positive integer between 1 and 10, is the order of the cavity, • n is the effective index of the cavity, and • <bl et 2 sont les déphasages à la réflexion sur les miroirs métalliques (déterminés par la nature des matériaux enjeu et la longueur d’onde considérée), • 0 is the angle of incidence of the incident light on the filter (counted from the perpendicular to the filter surface).

[0029] Once the cavity order has been chosen, the angle of attack known, the index and the phase shifts known, all that remains is to determine an approximate thickness h so that the cavity is centered on a particular wavelength. Once the filtering function has been calculated for each filter and each wavelength, the thicknesses h of the dielectrics are then adjusted according to the desired performance (search for a good signal-to-noise ratio, maximum transmission, etc.).

[0030] Another more empirical method consists of calculating, for several thicknesses h, the response of the stack and choosing h such that the resonance peak of the filter (Xres) is positioned in accordance with the specifications.

[0031] The invention relates to a method of manufacturing a multi-filter matrix tispectral, for an electromagnetic wave.

[0032] The electromagnetic wave received by the matrix can include wavelengths in the visible, infrared (near, medium or far) or microwave range.

[0033] In the following, the terms “Multispectral Filtering Matrix” and “Matrix” will be confused.

[0034] The matrix obtained by the method according to the invention comprises at least two color filters.

[0035] [Fig.2] is an example of a matrix 10 comprising three color filters Ft (here i is equal to 1, 2 and 3, it being understood that the matrix comprises at least two filters and may comprise more than three filters).

[0036] A color filter E is a filter that transmits only the said color when it receives an electromagnetic wave.

[0037] Optionally, each filter can be placed opposite a photoelectric transducer that can operate either as a collector of the light coming from the filters or as an emitter of light towards the filters. In the case of collectors, the transducers can be, for example, CMOS photodiodes. In the case of emitters, the transducers can be, for example, LED diodes, QLED diodes or LASER diodes, the emitters in this case having a broader emission spectrum than that of the corresponding Fabry-Pérot cavities.

[0038] Each filter E includes a first reflective layer C r n, a second reflective layer C^ and a layer of Fabry-Pérot cavity dielectric material Cppi between the two reflective layers (C r ii, C^i).

[0039] The terms “Fabry-Pérot cavity dielectric material layer”, “dielectric material layer” and “dielectric layer” will be confused in the rest of the article.

[0040] The thicknesses (h h2, h3) of the three layers of dielectric material C FPi of the three filters (Fi F2, F3) are different here. Thus, when each filter E receives an incident electromagnetic wave, it transmits a wavelength depending on the thickness E of its dielectric layer Cppid'according to the formula cited previously:

[0042] In the example of [Fig.2], the thickness hi of the dielectric layer C FP iof the first filterFi is less than the thickness h2 of the dielectric layer C FP2 of the second filter F2 which is itself less than the thickness h3 of the dielectric layer C FP3 of the third filter F3.

[0043] Each reflective layer (Cr H ,Cr2i ) of each filter E is preferably made of metal and has a metal mirror function. The metal is for example silver.

[0044] The upper surfaces Sl sup i and lower S l inf _i of the first reflective layer Crude each filter F ; are curved.

[0045] The upper surfaces S2 sup i and lower S2 inf i of the second reflective layer Cr 2i of each filter F, are also curved.

[0046] For each filter F b each layer of dielectric material C FPi has a surface area less than the contact S in f; of the first reflective layer Cr u and an upper surface S sup _i in contact with the second reflective layer Cr 2i .

[0047] Here, the lower surface S inf _i of the dielectric layer C m is in contact with the upper surface Slsup j of the first reflective layer Cr H . The radius of curvature of the upper surface Sl supJ of the first reflective layer Cr H is equal to the radius of curvature of the lower surface S inf _i of the CFR dielectric material layer.

[0048] Similarly, the upper surface S sup _j of the dielectric layer C FPi is in contact with the lower surface S2 in fj of the second reflective layer Cr 2i . The radius of curvature of the upper surface S2 inf j of the second reflective layer Cr 2i is equal to the radius of curvature of the upper surface of the dielectric material layer Cffi.

[0049] For each color filter F,, the curvatures of the lower surface S inf _i and the upper surface S sup _i of the dielectric material layer C FPiare both convex. The curvatures of the lower surface S l inL _i and the upper surface Sl sup _i of the first reflective layer Cr u and the curvatures of the lower surface S2 inf i and of the upper surface S2 sup _j of the second reflective layer Cr 2i are also convex.

[0050] When the upper surfaces S2, lip ; and lower S2 inf-i of the second reflective layer C r2i of an Fi filter are convex, the Fi filter allows the electromagnetic wave to be focused on the transducer T, opposite said filter F,, unlike a conventional state-of-the-art filter which requires a microlens above the Fabry-Pérot cavities in order to focus an incident wave.

[0051] Preferably, the radius of curvature of the lower surface S inf _i and the upper surface S sup_i of the dielectric material layer C FPi of each color filter F; is strictly greater than 300 nm.

[0052] The dielectric material of the dielectric material layer C FPi of each color filter F, is preferably but not limited to a material transparent in the visible range such as an organic material of the photosensitive polymer type modeled then hardened, or an inorganic material (oxide, silicon nitride, alumina, etc.). It should be noted that the invention is not limited to the visible range and that other materials transparent at other wavelengths, in the infrared for example (for example using silicon), can be used.

[0053] Each F; filter behaves like a material with a constant refractive index of 1.46, which is close to the refractive index of SiO2 which is 1.47 in the visible spectrum.

[0054] The thickness h; of the dielectric material layer Cm of each color filter F i is preferably substantially constant along said layer C FPi .

[0055] [Fig.3] is a representation of the spectral responses of the first Fi filter for a thickness hi of the dielectric layer at C equal to 100 nm and for several angles of incidence 0 of an incident electromagnetic wave. We thus note that for an angle of incidence 0 equal to 0°, 20° and 40°, the spectral responses of the first Fi filter are substantially identical and therefore do not depend on the angle of incidence of the wave.

[0056] [Fig.4] is a representation of the spectral responses of the second filter F2 for a thickness h2 of the dielectric layer at Cm equal to 120 nm and for several angles of incidence 0 of an incident electromagnetic wave. We thus note that for an angle of incidence 0 equal to 0°, 20° and 40°, the spectral responses of the second filter F2 are also substantially identical and therefore do not depend on the angle of incidence of the wave.

[0057] We notice in [Fig.3] and [Fig.4] that the two wavelengths transmitted by the first filter Fi and the second filter F2 respectively, are very different, in view of the two thicknesses (h t h2) different from the two dielectric layers (C FP i. C FP i) of the two filters.

[0058] When the array comprises at least three filters, the array comprises at least two different filters. "Two different filters" means two filters having two different respective dielectric layer thicknesses.

[0059] For example, an RGB type matrix might include 50% green color filters, 25% red color filters, and 25% blue color filters.

[0060] The matrix may comprise a number C x L of filters, C representing the number of columns of the 10 matrix and L representing the number of rows of the 10 matrix, L and C being two natural integers strictly greater than 0 with at least one of the natural integers L or C being greater than or equal to 2.

[0061] As a first approximation, we can consider that the lower surface S inL _i of the dielectric layer Cm of the filter F ;is substantially hemispherical even if other shapes can be considered. The same is true of the upper surface S sup _i of the dielectric material layer C FPi which can be considered as substantially hemispherical.

[0062] As illustrated in [Fig.5], the matrix 10 of [Fig.2] can be seen as a combination of two different layers 11 and 12. Layer 11 defines the lower curved surface S inf j, whose hemispherical shape of radius R o is the same for each filter Fi. In other words, layer 11 here comprises three protruding (i.e. convex) zones 11; of identical hemispherical shape and radius RO. Layer 12 defines the upper curved surface S supJ, whose substantially hemispherical shape has a different radius depending on the filter Fi considered. In other words, layer 12 has different hemispherical curvatures defined by three radii Ri, where i = 1, 2, 3... N where N is the number of filters (in the case of [Fig.4], N is equal to 3) in the matrix. Layer 12 here comprises three protruding (i.e. convex) zones 12; of hemispherical shape and of different respective radius R, (R b R2 and R3 being different here). For each Fabry-Pérot filter curve F b the radius R can be calculated using (for a hemispherical structure) the following formula: R, = Ro + t réflecte ur_bas+ h; (where i is equal to 1, 2 or 3) where t^fiecteu^bas is the thickness of the lower reflector (i.e. the first reflective layer) Cru of the filter F;.

[0063] Based on this decomposition, the applicant designed the manufacturing method according to the invention of a filter matrix as illustrated in [Fig.2].

[0064] The method according to the invention is based in particular on the use of two masks whose geometry and shape are obtained from layers 11 and 12 of [Fig.4].

[0065] To do this, according to one embodiment of the invention, the method firstly comprises a step of digital modeling of the two layers 11 and 12 in the form of digital targets UN and 12N of the layers 11 and 12 to be obtained. This digital modeling carried out before any manufacturing step makes it possible to ensure that there is good alignment between the respective zones lli and 12i which will subsequently define the curved Fabry-Pérot cavity filters of each pixel.

[0066] From these 1 IN and 12N digital targets, a 1 IL and 12L mask layout can be generated, respectively for the UN and 12N targets, which can be used in electronic or optical grayscale lithography. Grayscale lithography is a lithography allowing the production of complex three-dimensional shapes in a photosensitive resin. The mask used in Grayscale lithography is generally composed of under-resolved or limit-resolution chrome patterns. This type of pattern allows a local modification of amplitude to the incident illumination on the resin. The resin being spatially exposed to a variable dose, its dissolution rate is modified locally.The development rate of a resin (negative or positive) being proportional to its degree of dissolution in the developer, it is possible to obtain complex 3D shapes by precisely controlling the dose received by each point of the resin. For the production of the Grayscale mask, the size of the chrome pads is generally used to obtain the shape of the desired patterns. Thus, according to the present invention, each mask design 11L and 12L here comprises three groups HMi and 12Mi each including a plurality of patterns m substantially. chrome square of variable size, each group 11 Mi and 12Mi being intended to respectively form the zones 1 li and 12i of layers 11 and 12.

[0067] Once the designs of the 1 IL and 12L masks are made, it is possible to manufacture the corresponding IIP and 12P physical masks, illustrated in [Fig.7]. The 1 IP and 12P masks are then each used for a Grayscale lithography step on a resin layer in order to obtain two three-dimensional structured resin layers 11 PM and 12PM, called master structures, identical to the two layers 11 and 12.

[0068] Each master structure 11PM and 12PM is then used to make a printing mold, respectively, 13 and 14.

[0069] The first printing mold 14 corresponding to the master structure 12PM comprises at least two cavities E11 (here three cavities E11, E12 and E13) of concave shape. Each cavity E11 has a surface substantially of hemispherical shape of radius Ri as defined previously. It will be noted that the base Bi of each cavity is preferably circular but could also have a different shape.

[0070] The second printing mold 13 corresponding to the master structure 11PM comprises at least two cavities E2i (here three cavities E21, E22 and E23) of concave shape. Each cavity E2i has a surface substantially of hemispherical shape of radius R0 as defined previously. The radius R0 is identical for each cavity E2i. It will be noted that the base of each cavity is preferably circular but could also have a different shape.

[0071] The first and second printing molds 14 and 13 are obtained by techniques known to those skilled in the art respectively from the master structures 12PM and 11PM. The molds 14 and 13 can for example be obtained by the following steps: • spreading by spin coating of a resin on the master structure so that the resin is structured by the patterns of the master structure; • depositing a layer of flexible polymer film in contact with the resin coated by lamination; • crosslinking of the resin using one or more parameters including UV exposure, annealing temperature, specific crosslinking pressure; • detachment of the flexible polymer film layer on which the parent resin is attached by lamination.

[0072] This gives the first and second printing molds 14 and 13 which are here flexible molds which can be used subsequently during nano- printing. Note that the spin coating step can be preceded by a step of depositing a non-stick layer on the master structure.

[0073] The resins used for molds 14 and 13 can be, for example, resins of the mr-NIL210 type (UV crosslinking) or mr-NIL6000E (UV and temperature crosslinking).

[0074] [Fig.8] illustrates the different stages of the method 100 according to the invention for manufacturing the multispectral filtering matrix of [Fig.2] using the two molds 14 and 13

[0075] The first step 101 consists of depositing, for example by spin coating, a layer of resin 201 on a carrier substrate 200. The carrier substrate 200 may for example be a Si substrate, a Silicon On Insulator (SOI) substrate or a glass or sapphire substrate. This step includes, if necessary, a step of hardening the resin by annealing. It should be noted that it is also possible to have photoelectric transducers under or in the substrate.

[0076] The second step 102 of the method 100 consists of structuring the resin layer 201 to obtain a plurality of patterns Mi of structuring material, each resin pattern having a curved upper surface. According to the invention, at least two patterns are necessary, three patterns M1, M2 and M3 being shown in [Fig. 8]. Each resin pattern Mj has a curved upper surface of hemispherical shape and radius R0. The structuring is here carried out by a nano-imprinting technique using the second mold 13 previously produced. As a reminder, the mold 13 has a plurality of hemispherical concave imprints of radius R0. The choice of resin will depend on the type of nano-imprinting used (UV-assisted, thermal, pressure-assisted, etc.). In the event that photoelectric transducers are present, the patterns Mi are each produced opposite a photoelectric transducer.

[0077] It will be noted that, according to step 102, the structuring of the resin can alternatively be carried out by an electronic or optical grayscale lithography method (followed by stabilization of the Grayscale resin by thermal or ultraviolet process).

[0078] The third step 103 of the method 100 according to the invention consists of depositing, in a conformal manner, a first reflective layer 203 on the patterns Mi. The first reflective layer 203 forms the first reflective layer Cr H of each color filter F;

[0079] The reflective layer is preferably deposited continuously by plasma-enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD), pulsed laser deposition (PLD) or deposition of atomic thin layers ALD (atomic layers deposition) for example.

[0080] The fourth step 104 of the method 100 according to the second aspect of the invention consists of depositing a layer of dielectric material 204 on the first reflective layer 203. The dielectric material is the material intended to form the layers of dielectric material of the Fabry-Pérot cavity of the Fi filters.

[0081] Steps 105 and 106 then consist of structuring the layer of dielectric material 204 by nano-imprinting using the first mold 14 so as to obtain a plurality of layers of dielectric material C m of Fabry-Pérot comprising a lower surface in contact with the first reflective layer 203. As mentioned above, the first mold 14 was sized for: • That the Eli prints of mold 14 are opposite the Mi patterns; • That the Eli impressions of mold 14 have a hemispherical shape of radius Ri = RQ + reflector-ba S+ L (where i is equal to 1, 2 or 3) where ^ur-bas is the thickness of the lower reflector (i.e. the first reflective layer 203) and R0 is the radius of each resin pattern Mj having a curved upper surface of hemispherical shape so as to obtain a plurality of layers of dielectric material C FPi (here 3) of Fabry-Pérot of height hi (here, hl, h2 and h3 with hl less than h2 less than h3) different as illustrated in step 106.

[0082] The dielectric material is a nanoimprint resin such as an organic dielectric material. The volume of the nanoimprint material that also serves as the cavity material for the curved Fabry-Pérot filter (i.e., the volume of the dielectric material layer 204) can be calculated by taking the volume difference between the master structure 14 and the master structure 13. Here, we have given an example of a hemispherical 3D curved surface for the master structures. Consider an individual pixel size of a pixelated filter array of length Px in the horizontal direction and width Py in the vertical direction as shown in Figure 9. Consider that the filters are arranged in a matrix having a total of N = nxn filters. For the master structure 14, the volume can be calculated as follows:

[0083] where Ri is the radius of the hemisphere of the master structure 14 corresponding to pixel i.

[0084] Similarly, for master structure 13, the volume can be calculated as follows:

[0085] where R0 is the constant radius of each hemisphere of the master structure 13.

[0086] The volume V of the nanoimprint material which also serves as the cavity material for the curved Fabry-Pérot filter can then be calculated as follows:

[0087] where ho is the equivalent thickness of material if the latter is deposited in a planar manner.

[0088] Step 107 finally consists of depositing a second reflective layer 205 on the layers of dielectric material C FPi to form the second reflective layer C R2i of the Fi filters.

[0089] As already mentioned previously, in addition to the reduced number of selective deposition and selective etching steps required for the production of curved filters with different thicknesses, another advantage of the method according to the invention is that the nano-imprint mold(s) can be used several times, thus reducing the manufacturing cost.

Claims

Claims

1. A method (100) of manufacturing a multispectral filtering matrix for an electromagnetic wave, the matrix comprising at least a first and a second color filter (F1, F2, F3), each color filter forming a Fabry-Pérot cavity comprising a first reflective layer (CRU, CR12, CR13), a second reflective layer (CR21, CR22, CR23) and a layer of Fabry-Pérot cavity dielectric material (CFP1, CFP2, CFP3) between the first reflective layer and the second reflective layer, the layer of dielectric material comprising: - a lower surface in contact with the first reflective layer, the lower surface being curved; - an upper surface in contact with the second reflective layer, the upper surface being curved; the thicknesses (hl, h2, h3) of the two layers of dielectric material of the two color filters being different, said method being implemented by means of at least one printing mold and comprising the following steps: - Deposition (101) on a substrate of a layer of structuring material; - Structuring (102) the layer of structuring material, to obtain a first pattern of structuring material and a second pattern of structuring material, each pattern having a curved upper surface; - Conformal deposition (103) of a first reflective layer on the first and second patterns, forming the first reflective layers of the first and second color filters; - Deposition (104) of a layer of dielectric material on the first reflective layer, the lower surface of the dielectric layer covering the curved upper surfaces of the first and second patterns coated with the first reflective layer so as to form the curved lower surfaces of the layers of Fabry-Pérot cavity dielectric material of the first and second filters; Structuring (105, 106) the layer of dielectric material by nano-imprint lithography using the printing mold comprising at least two different curved imprints configured to form the curved upper surfaces of the layers of Fabry-Pérot cavity dielectric material of the first and second filters so as to obtain different thicknesses of the two layers of dielectric material; Conformal deposition (107) of a second reflective layer on the layer of dielectric material forming the second reflective layers of the first and second color filters.

2. Method (100) according to the preceding claim characterized in that the printing mold is produced by Grayscale grayscale lithography.

3. Method (100) according to the preceding claim characterized in that the production of the printing mold comprises the following steps: - Fabrication by grayscale lithography of a master structure (12PM, 11 PM) comprising at least two convex curved patterns; - spreading a resin on the master structure so that the resin is structured by the patterns of the master structure; - depositing a layer of flexible film in contact with the structured resin; - crosslinking of the structured resin; - detachment of the flexible film layer on which the structured resin is attached in order to obtain the printing mold (14, 13).

4. Method according to one of the preceding claims, characterized in that the mold impressions are concave impressions having a surface substantially in the shape of a portion of a sphere.

5. Method according to one of the preceding claims, characterized in that the step of structuring the layer of structuring material, to obtain a first pattern of structuring material and a second structuring material pattern is produced by nanoimprint lithography using a second mold comprising at least two identical curved imprints configured so as to obtain an identical shape for the upper surfaces of the first and second patterns.

6. Method according to claim 5 characterized in that the at least two cavities of the first mold have a surface substantially in the form of a portion of a sphere of identical radius and the at least two cavities of the second mold have a surface substantially in the form of a portion of a sphere of different radius.

7. Method according to one of claims 5 or 6 characterized in that the volume of the dielectric material of the layer of dielectric material is determined by the difference between the sum of the volumes of the imprints of the first mold and the sum of the volumes of the imprints of the second mold.

8. Method according to one of claims 1 to 3 characterized in that the step of structuring the layer of structuring material, to obtain a first pattern of structuring material and a second pattern of structuring material is carried out by Grayscale grayscale lithography.

9. Method according to one of the preceding claims, characterized in that each color filter is formed opposite a photoelectric transducer.

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