Method for manufacturing a multispectral filter for electromagnetic radiation

Abstract

Method for manufacturing a multispectral filter for electromagnetic radiation The invention relates to a method (100) for manufacturing a multispectral filter for electromagnetic radiation comprising at least two filters, each filter comprising a first reflective layer, a second reflective layer, a dielectric layer of Fabry-Pérot cavity, the method comprising the steps of: Deposition (101) on a carrier substrate comprising at least two photoelectric transducers, of a layer of structuring material; Structuring (101) in 3D of the layer of structuring material so as to obtain at least two patterns of different heights, one of the patterns having a maximum reference height relative to the carrier substrate; Conformal deposition (104) of a first reflective layer; Deposition (105) of a layer made in the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities;Planarization (106) by removing the dielectric material with selective stopping at the top of the highest structuring material pattern; Deposition (107) of a layer made of the same dielectric material so as to finalize the formation of the Fabry-Pérot cavities and of a second reflective layer on the two Fabry-Pérot cavities. Figure to be published with the abbreviation: Figure 1;

Description

Title of the invention: Method for manufacturing a multispectral filter for electromagnetic radiation 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 colored filters 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 filter for electromagnetic radiation. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] A spectral filter or a color filter makes it possible to filter light by wavelength, so as to provide information on the intensity of the light in certain wavelengths. Several color filters can be combined to form, for example, red-green-blue filters (RGB in English terminology) 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. 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 remainder of the incident light is reflected.Generally speaking, the thickness of the dielectric layer sets the transmitted central 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 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. This entails significant technological constraints, in particular at least one masking and then etching step for each dielectric cavity produced.

[0005] It has also been shown that it is possible to use a network of multispectral filters for imaging directly produced on an array of optical sensors using a CMOS-compatible manufacturing technique (bottom-up approach in English terminology).

[0006] More recently, the feasibility of optically functional devices following the creation of Fabry-Pérot cavities above a CMOS image sensor device using a grayscale lithography technique has also been described in GB2574805. The manufacturing process of the multispectral filter in this document is based on the following steps: • Deposition of a first metal layer on a substrate comprising CMOS type photoelectric transducers; • Structuring of a resin layer by Grayscale lithography so as to create a plurality of resin patterns, each pattern forming a Fabry-Pérot cavity; • Deposition of a second layer of metal on the patterns.

[0007] This latter solution also has certain disadvantages. The first of these consists of carrying out Grayscale lithography on a stack already comprising a metal layer: a reflection phenomenon at the metal-resin interface is then likely to greatly affect the control of the resist thickness during lithography. In addition, Grayscale lithography makes it possible to obtain minimum resist pattern thicknesses of 40 or 50 nm: such a value is sufficient in the visible range but it may be necessary to obtain lower thicknesses to filter lower wavelengths in other spectral ranges. Such thicknesses below 40-50 nm are difficult to obtain with the use of Grayscale lithography as described in document GB2574805. Summary of the invention

[0008] The invention provides a solution to the problems mentioned above, by proposing a method for manufacturing a multispectral filter for electromagnetic radiation making it possible to better control the thicknesses of the Fabry-Pérot cavities and to obtain Fabry-Pérot cavity thicknesses of less than 40 nm.

[0009] To this end, the invention relates to a method for manufacturing a multispectral filter for electromagnetic radiation, said filter comprising at least two color filters, each filter comprising a first reflective layer, a second reflective layer, a layer of Fabry-Pérot cavity dielectric material between the first reflective layer and the second reflective layer, the thickness of the dielectric layer of the two color filters being different and each of the two filters being opposite a photoelectric transducer, said method comprising the following steps: • Deposition on a carrier substrate comprising at least two photoelectric transducers, of a layer of structuring material; • Three-dimensional structuring of the layer of structuring material so as to obtain at least two patterns of structuring material of different heights, at least one of the patterns having a maximum reference height relative to the carrier substrate, the height being measured perpendicular to the plane of the substrate, each of the patterns being opposite a photoelectric transducer; • Conformal deposition of a first reflective layer on the at least two patterns of structuring material; • Deposition of a layer made in the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities, said layer of dielectric material covering all of the patterns by presenting an upper surface of which each point is located at a height greater than the maximum reference height; • Planarization by removal of the dielectric material with selective stopping at the top of the highest structuring material pattern covered with the reflective layer; • Deposition of a layer made from the same dielectric material in order to finalize the formation of the Fabry-Pérot cavities; • Deposition of a second reflective layer on at least two Fabry-Pérot cavities.

[0010] Thanks to the invention, the Fabry Pérot cavities are produced with a structuring step, for example via Grayscale lithography, carried out before the step of depositing the first reflective layer. This characteristic makes it possible to avoid the drawbacks linked to the phenomenon of reflection at the metal-resin interface. In addition, the thickness of the cavity of the smallest thickness is directly fixed by the thickness of the dielectric layer produced during the second deposition of dielectric material directly on the first reflective layer. Indeed, this deposition is preceded by a planarization step with a stop on the top of the pattern of structuring material covered with the reflective layer: thus, it is indeed the thickness of the second layer of dielectric material which makes it possible to fix the thickness of the smallest Fabry-Pérot cavity.By proceeding in this way, the method according to the invention overcomes the thickness control limits linked to Grayscale lithography, and allows, by conventional deposition techniques, to achieve thicknesses much lower than those of known solutions, in particular less than 40 nm. Finally, it should be noted that the method according to the invention applies to any type of substrate, whether they are . substrate incorporating CMOS photodetectors or transparent substrate, for example made of glass, the photodetectors being for example arranged under the substrate. In this respect, the term "carrier substrate" means both the substrate and the photoelectric transducers, whether the latter are integrated into the substrate or above or below said substrate.

[0011] The term “photoelectric transducers” means devices which can operate either as a collector of light from the filters or as an emitter of light towards the filters. In the case of collectors, the transducers may be, for example, CMOS photodiodes. In the case of emitters, the transducers may 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.

[0012] In addition to the characteristics which have just been mentioned in the preceding paragraph, the method of the invention may have one or more additional characteristics among the following, considered individually or according to all technically possible combinations: • According to a first embodiment, the structuring material is a resin, said structuring step being carried out by a grayscale lithography step on the layer of structuring material followed by a step of crosslinking the resin; advantageously, the structuring step is followed, before the step of conformal deposition of the first reflective layer on the at least two patterns of structuring material, by a step of conformal deposition of an encapsulation layer on the at least two patterns of structuring material, said first reflective layer covering the encapsulation layer; • According to a second embodiment, said structuring material is an organic or inorganic insulating material, said structuring step comprising the following sub-steps: • Deposition of a layer of resin following the step of deposition of the layer of organic or inorganic insulating material; • Grayscale lithography on the resin layer in order to structure the resin layer in three dimensions to obtain at least two resin patterns of different heights; • Transfer of the two resin patterns into the layer of organic or inorganic material so as to obtain said at least two patterns of structuring material of different heights. • the deposition of the layer made in the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities and the deposition of a layer made in the same dielectric material so as to finalize the formation Fabry-Pérot cavities are conformal deposits; the step of three-dimensional structuring of the layer of structuring material is a step of obtaining at least two patterns of structuring material of different heights having an empty space between said at least two structuring patterns. According to a first variant, the method according to the invention comprises, after the step of conformal deposition of the first reflective layer and before the deposition of the layer produced in the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities, the following steps: • Deposition of a layer, called an insulating layer, said insulating layer covering all of the structuring material patterns by presenting an upper surface of which each point is located at a height relative to the carrier substrate greater than the maximum reference height; • Deposition of a layer of resin above said insulation layer; • Removal of the resin in order to keep the resin only above of the empty space(s) between the structuring material patterns and leave the insulation layer exposed above the structuring material patterns; • Removal of the insulation layer material in the exposed area of ​​the insulation layer; • Removal of the remaining resin in order to preserve walls made of said material of the insulation layer between the patterns of structuring material. According to a second variant, the method according to the invention comprises, after the step of conformal deposition of the first reflective layer and before the deposition of the layer produced in the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities, the following steps: • Deposition of a layer of resin covering all of the structuring material patterns, presenting an upper surface where each point is located at a height relative to the supporting substrate greater than the maximum reference height; • Removing the resin between the structuring material patterns in order to keep the resin only above the structuring material patterns; • Deposition of a layer, called an insulating layer, said insulating layer covering all of the patterns of structuring material covered with resin and filling the spaces between said patterns, by presenting an upper surface of which each point is located at a height relative to the supporting substrate greater than the maximum reference height; • Removing the insulation layer material located above the structuring material patterns and the remaining resin in order to maintain walls made of said insulation layer material between the structuring material patterns; said material of the insulation layer may be a sacrificial material; said method then comprising the following steps: • Deposition of a layer of resin on the second reflective layer; • Removal of resin in areas above the space(s) between the structuring material patterns; • Removing the material of the second reflective layer, the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities and the sacrificial material in the areas above the space(s) between the structuring material patterns so as to form void walls between the structuring material patterns and between the Fabry-Pérot cavities overhanging them; • Removal of remaining resin. said material of the insulation layer may also be a dielectric material with a low or high optical index; by material with a high or low optical index is meant a material having an optical refractive index strictly lower or strictly higher than the refractive index of the resin or of the material of the underlayer and the refractive index of the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities; said method then comprises the following steps: • Deposition of a layer of resin on the second reflective layer; • Removal of resin in areas above the space(s) between the structuring material patterns; • Removal of the material of the second reflective layer and the dielectric material in the areas not protected by the remaining resin in order to access the dielectric material with low or high optical index; • Deposition of a layer of dielectric material with low or high optical index above the remaining resin and supplementing the dielectric material already present between the structuring material patterns so as to fill the void between the Fabry-Pérot cavities overhanging them; • Removal of the resin and the low or high optical index dielectric material above the resin areas, leaving the low or high optical index material between the structuring material patterns and between the Fabry-Pérot cavities overhanging them so as to form dielectric insulation walls.

[0013] 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

[0014] The figures are presented for information purposes only and in no way limit the invention. • [Fig.l] illustrates the different stages of the method according to a first embodiment of the invention; • [Fig.2] illustrates the different stages of the method according to a second embodiment of the invention; • [Fig.3], [Fig.4], [Fig.5], [Fig.6], [Fig.7], [Fig.8] and [Fig.9] illustrate the different stages of two variants of the method according to the invention making it possible to ensure optical isolation between the pixels as well as between the Fabry-Pérot cavities. DETAILED DESCRIPTION

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

[0016] It should be recalled beforehand 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 dimensioning 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.

[0017] 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 the English terminology).

[0018] These calculation programs allow the optimal parameters of the 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: mk--

[0019] where • 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 •<pl et q> 2 are the phase shifts on reflection on metal mirrors (determined by the nature of the materials involved and the wavelength considered), • 0 is the angle of incidence of the incident light on the filter (counted from from the perpendicular to the filter surface).

[0020] Once the cavity order is chosen, the angle of attack is known, the index and the phase shifts are 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 is 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.).

[0021] 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.

[0022] [Fig.l] illustrates the different steps of a method 100 according to a first embodiment of the invention in which no insulation is provided either between the Fabry-Pérot cavities or between the photoelectric transducers.

[0023] The first step 101 of the method 100 consists of depositing on a substrate 200, called the carrier substrate, a layer of resin 201 and then structuring said layer of resin 201 in three dimensions. The substrate 200 can for example be an Si substrate, a Silicon on Insulator SOI substrate (for “Silicon On Insulator” according to the English terminology) or a glass or sapphire substrate.

[0024] The carrier substrate 200 comprises a plurality of (at least two) photoelectric transducers 202Ai (here 3 photoelectric transducers 202A1, 202A2, and 202A3 are shown). The transducers 202Ai are shown here schematically under the substrate 200, it being understood that they could be formed inside the latter or above the latter. According to the invention, the photoelectric transducers 202Ai are considered to be an integral part of the carrier substrate 200. The photoelectric transducers can operate either as a collector of light coming from the filters or as an emitter of light towards the filters. If they are collectors, the transducers can be for example CMOS type photodiodes. If they are emitters, the transducers can be for example LED diodes, QLED type diodes or LASER diodes, the emitters in this case having a broader emission spectrum than that of the corresponding Fabry-Pérot cavities.

[0025] The 3D structuring of the resin layer 201 is carried out by a lithography step. This lithography may preferably be a grayscale lithography according to the English electronic or optical terminology. Other lithography techniques such as two-photon lithography or nanoimprint lithography may also be used for producing the resin structure 201. The structure 201 comprises a plurality of 3D patterns 203Ai (here 3 patterns 203A1, 203A2, and 203A3). It is possible to freely fix the dimensions of each pattern in the three directions of the Oxyz space (where Oxy is the plane of the figure, the Oy axis being in the direction perpendicular to the plane of the substrate 200 and the Oz axis being in the direction perpendicular to the plane of the figure).

[0026] According to the invention, it is appropriate to have at least two resin patterns 203Ai of different heights (here the 3 patterns each have different heights). Among all of these patterns 203Ai, one of them, here the pattern 203A1, has a maximum height Hmax, called reference, the height being measured perpendicular to the plane of the substrate 200 along the axis Ox. More generally, the height of the pattern 203Ai will be noted hresist i. Thus, in [Fig.l], Hmax is equal to hresist-i- Each pattern 203Ai is opposite along the axis Oy the corresponding transducer 202Ai.

[0027] The method 100 then comprises a step 102 of crosslinking (cross-linking) the structured resin layer 201 in order to densify the latter via stabilization of the Grayscale resin by thermal or ultraviolet process.

[0028] Advantageously, the method 100 according to the invention comprises a third step 103 consisting of carrying out a conformal deposition of a thin encapsulation layer 204 (a few tens of nm) on the resin patterns 203Ai (above and on the sides of the patterns 203Ai). The material of the encapsulation layer 204 may be for example an oxide of the Al2O3 or SiO2 type or a nitride and the deposition will preferably be carried out by a low-temperature deposition technique such as an atomic layer deposition (ALD) according to the English terminology.

[0029] The method 100 according to the invention then comprises a step 104 of depositing a reflective layer 205, for example with a thickness of between 20 and 100 nm, covering the encapsulation layer 204 above the resin patterns 203Ai. This reflective layer 205, typically a metal layer, forms the first reflective layer of the future Fabry-Pérot cavity type color filters. The reflective layer 205 is deposited conformally by chemical vapor deposition (CVD) or physical vapor deposition (PVD). The layer 205 is deposited continuously on all of the resin patterns 203Ai covered with the encapsulation layer, including on the sides of the latter. The conformal deposition makes it possible to have a constant thickness of the reflective layer 205, at least on the top of the patterns but also preferentially on the sides of the patterns 203Ai.

[0030] The following step 105 consists of depositing a layer 206 made of the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities. The layer 206 of dielectric material covers all of the resin patterns 203Ai covered with the encapsulation 204 and reflective 205 layers. The layer 206 has an upper surface 207 (not necessarily flat) each point of which is located at a height, relative to the carrier substrate 200, greater than the maximum reference height Hmax. The material of the layer 206 is preferably but not limited to a material transparent in the visible range such as an organic material of the polymer or inorganic type (oxide, silicon nitride, alumina, etc.).The deposition is preferably a conformal deposition, for example carried out by a physical vapor deposition (PVD) technique or a chemical vapor deposition (CVD) technique or a low pressure chemical vapor deposition (LPCVD) technique or a plasma-enhanced chemical vapor deposition (PECVD) technique. It should be noted that the invention is not limited to the visible range and that other materials transparent to other wavelengths, in the infrared for example (for example using silicon), may be used.

[0031] The method 100 then comprises a step 106 of planarization of the layer 206 made in the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities so as to form a surface-planarized layer 208 by removal of the dielectric material from the layer 206. The planarization step can be carried out by an etch-back type etching step and / or a CMP (Chemical Mechanical Polishing) step. The planarization is carried out with a stop on the reflective layer 205 located at its highest level (i.e. at the level of the reference height of the pattern 203A1).

[0032] The method 100 according to the invention then comprises a step 107 of conformal deposition of a layer 209 of the same dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities as during step 105. This step is for example carried out by a technique of physical vapor deposition PVD (Physical Vapor Deposition) or chemical vapor deposition CVD (Chemical Vapor Deposition in English) or low pressure chemical vapor deposition LPCVD (Low Pressure Chemical Vapor Deposition in English) or chemical vapor deposition vapor assisted by plasma PECVD (Plasma Enhanced Chemical Vapor Deposition in English). The height of the layer 209 is noted hc, the height being measured perpendicular to the plane of the substrate. After this step, a plurality of Fabry-Pérot cavity dielectric patterns 204Ai are obtained (here three patterns 204A1, 204A2 and 204A3).

[0033] For each resin pattern 204Ai, hdiel_i denotes the height of the pattern, the height being measured perpendicular to the plane of the substrate. The height hdiel_i of the pattern 204i can be determined according to the methods mentioned above (depending on the specifications for the desired filtering). According to the method 100 according to the invention, the height hdiel_i is fixed by the following formula: hdiel_i = Hmax - hresist i + hc.

[0034] Thus, for pattern 204A1, hdiel_l is here directly equal to the height hc of layer 209.

[0035] More generally, for each pattern 204Ai, the height is technologically determined by the difference in height between that of the highest 203Al resin pattern Hmax and the height of the 203Ai resin pattern to which the height of the second dielectric layer 209 is added. It is thus observed that the height of the 204Ai Fabry-Pérot cavity dielectric patterns is not linked to the thickness of the resin layer 201 (unlike the solutions of the state of the art which make it difficult to obtain thicknesses of around ten nm) but to the difference in height between the patterns. Such a configuration makes it possible to achieve much smaller heights.This is particularly true for the Fabry-Pérot cavity dielectric pattern 204A1 formed directly above the uppermost resin pattern 203Al which depends only on the height of the second dielectric layer 209 which is very easily controllable and can reach values ​​of the order of 10 nm.

[0036] Step 108 of the method 100 then consists of depositing a second reflective layer 210, for example with a thickness of between 20 and 50 nm, covering the second dielectric layer 209 above the Fabry-Pérot cavity patterns 204Ai. This planar reflective layer 210 forms the second reflective layer of the Fabry-Pérot cavity type color filters. The reflective layer 210 is deposited conformally by chemical vapor deposition (CVD) or physical vapor deposition (PVD). This produces a plurality (here 3) of Fabry-Pérot cavity type color filters Fi (i.e. F1, F2 and F3), each formed by the first reflective layer 205, the pattern 204Ai and the second reflective layer 210.

[0037] Optionally, it is also possible to deposit a layer 211 according to CMOS technology on the second reflective layer 210.

[0038] [Fig.2] illustrates the different stages of a method 300, an alternative to the method 100 of [Fig.l], in which no insulation is provided between the Fabry-Pérot cavities nor between the photoelectric transducers.

[0039] The first step 301 of the method 300 consists of depositing on a substrate 400, called the carrier substrate, a layer of material such as an organic material of the polymer or inorganic type (oxide, silicon nitride, alumina, called the sub-layer 401. The substrate 400 is of the same type as the substrate 200 of [Fig.l] and comprises a plurality of photoelectric transducers (at least two) 402Ai (here 3 photoelectric transducers 402A1, 402A2, and 402A3 are shown). A layer of resin 412 is then deposited on the sub-layer 401. The layer of resin 412 is then structured in three dimensions. The 3D structuring of the layer of resin 412 is carried out by a lithography step. This lithography can preferably be a grayscale lithography or Grayscale according to the English electronic terminology or optical.Other lithography techniques such as two-photon lithography or nano-imprinting can also be used to produce the resin structure 412. The structure 412 comprises a plurality of 3D patterns 412Ai (here 3 patterns 412A1, 412A2, and 412A3). It is possible to freely fix the dimensions of each pattern in the three directions of the Oxyz space (where Oxy is the plane of the figure, the Oy axis being in the direction perpendicular to the plane of the substrate 400 and the Oz axis being in the direction perpendicular to the plane of the figure).

[0040] According to the invention, it is appropriate to have at least two resin patterns 412Ai of different heights (here the 3 patterns each have different heights). Among all of these patterns 412Ai, one of them, here the pattern 412A1, has a maximum height Hmax, called reference, the height being measured perpendicular to the plane of the substrate 400 along the axis Ox. More generally, the height of the pattern 412Ai will be noted hresist_i. Thus, in [Fig.2], Hmax is equal to hresist_i. Each pattern 412Ai is opposite along the axis Oy the corresponding transducer 202Ai.

[0041] The method 300 then comprises a step 302 of transferring the patterns 412Ai from the structured resin layer 412 into the sub-layer 401: in other words, at the end of this step 302, the structured resin layer 412 is removed and entirely transferred into the sub-layer 401 so that the sub-layer 401 is itself structured in three dimensions with a plurality of patterns 403Ai (here three patterns 403A1, 403A2 and 403A3) of dimensions similar to the dimensions of the patterns 412Ai. This transfer step can be carried out using techniques known to those skilled in the art such as dry etching or wet etching.

[0042] Step 302 is followed by a step 303 of depositing a reflective layer 405, for example with a thickness of between 20 and 50 nm, covering the patterns 403Ai of the structured sub-layer 401. This reflective layer 505 forms the first reflective layer of the future Fabry-Pérot cavity type color filters. The reflective layer 505 is deposited conformally by chemical vapor deposition. CVD (Chemical Vapor Deposition in English) or physical vapor deposition PVD (Physical Vapor Deposition). The layer 405 is continuously deposited on all of the patterns 403Ai, including on the sides of the latter. The conformal deposition makes it possible to have a constant thickness of the reflective layer 405, at least on the top of the patterns but also preferentially on the sides of the patterns 403Ai. It will be noted that, unlike the first embodiment of [Fig.l], it is here entirely possible to dispense with the deposition of an encapsulation layer. As for the first embodiment of [Fig.l], the structuring step, using for example Grayscale lithography, is carried out before the step of deposition of the first reflective metal layer.

[0043] The advantage of having patterns that are not made of resin but of another organic or inorganic material lies in the fact that the resin is often a polymer resin which can have characteristics that degrade over time, resulting in a change in color or loss of light transmission. The use of an organic material allows for better stability over time and the use of an organic material makes it possible to avoid a change in color over time.

[0044] Steps 304 to 307 of the method 300 according to the invention are identical to steps 105 to 108 of the method 100 according to the invention.

[0045] Thus, the following step 304 consists of depositing a layer 406 made of the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities. The layer 406 of dielectric material covers all of the patterns 403Ai covered with the reflective layer 405. The layer 406 has an upper surface 407 (not necessarily flat) each point of which is located at a height, relative to the carrier substrate 400, greater than the maximum reference height Hmax. The material of the layer 406 is preferably but not limited to a material transparent in the visible range such as an organic material of the polymer or inorganic type (oxide, silicon nitride, alumina, etc.).The deposit is preferably a conformal deposit, for example carried out using a physical vapor deposition technique (PVD) or chemical vapor deposition (CVD) or low pressure chemical vapor deposition (LPCVD) or plasma-enhanced chemical vapor deposition (PECVD).

[0046] The method 400 then comprises a step 305 of planarization of the layer 406 made in the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities so as to form a surface-planarized layer 408 by removal of the dielectric material from the layer 406. The planarization is carried out with stopping on the reflective layer 405 located at its highest level (i.e. at the level of the reference height of the pattern 403A1).

[0047] The method 300 according to the invention then comprises a step 306 of conformal deposition of a layer 409 of the same dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities as during step 304. This step is for example carried out by a PVD, CVD, LPCVD or PECVD deposition technique. The height of the layer 409 is noted hc, the height being measured perpendicular to the plane of the substrate. After this step, a plurality of dielectric patterns of Fabry-Pérot cavity 404Ai are obtained (here three patterns 404A1, 404A2 and 404A3).

[0048] For each resin pattern 404Ai, its height hdiel_i is determined in an identical manner to the case of method 100 of [Fig.l].

[0049] Step 307 of method 300 then consists of depositing a second reflective layer 410, for example with a thickness of between 20 and 50 nm, covering the second dielectric layer 409 above the Fabry-Pérot cavity patterns 404Ai. This planar reflective layer 410 forms the second reflective layer of the Fabry-Pérot cavity type color filters. The reflective layer 410 is deposited conformally by CVD or PVD deposition. A plurality (here 3) of Fabry-Pérot cavity type color filters Fi (i.e. F1, F2 and F3) are thus obtained, each formed by the first reflective layer 405, the pattern 404Ai and the second reflective layer 410.

[0050] Optionally, it is also possible to deposit a CMOS layer 411 on the second reflective layer 410.

[0051] The embodiments of Figures 1 and 2 illustrate the simple and efficient fabrication of Fabry-Pérot resonant cavities. However, in the case of photoelectric transducers present in a discrete manner, i.e. pixelated transducers, each pixel being formed by a photoelectric transducer (a photodetector for example) and the corresponding Fabry-Pérot cavity, it may be particularly advantageous to achieve optical isolation between each pixel. Indeed, when the dimensions of the pixels and therefore of the color filters are reduced, typically of the order of the wavelength of the light, the spatial overlap of the light contributions from one Fabry-Pérot cavity to another can degrade the efficiency of the overall device. This “crosstalk” phenomenon has already been observed for photoelectric transducers (i.e. CMOS sensors).In recent years, pixel dimensions have been steadily shrinking, in order to offer high-resolution sensors, particularly for smartphones. This reduction in pixel dimensions has two very distinct consequences: . The total amount of incident light arriving at each pixel decreases, implying that fewer and fewer photons reach the photo component sensitive. The collection and proper guidance of each photon within the component to the sensor is all the more important to ensure the good efficiency of the sensor. • When the pixel size approaches the length of the light to be collected, diffraction comes into play, which increases optical and spatial losses in the device.

[0052] Accompanying the issues related to the reduction of pixel dimensions, the angle of incidence with which light enters the Fabry-Pérot cavity is also an element that should not be neglected. Indeed, when oblique light rays reach the surface of the cavities, a certain part of the light passes through the physical edge of the filter, to end its course in the neighboring cavity. This unwanted, parasitic contribution distorts the light collection at the device scale, and is another important source in the "crosstalk" from one pixel to another.

[0053] [Fig. 3] schematically shows a carrier substrate 500 in top view and in section along the plane P perpendicular to the plane of the substrate 500 and intersecting the photoelectric transducers. The carrier substrate 500 comprises a plurality of pixelated photoelectric transducers 502Ai arranged in the form of a matrix (here a 3x3 matrix) in the substrate 500 (three of which 502A1, 502A3 and 502A3 are shown in section) included in the substrate 500. The substrate 500 is covered with a barrier layer 501.

[0054] We will now describe different variants of the method according to the invention making it possible to produce color filters, each associated with a transducer located above or in the substrate 500, with optical isolation making it possible to reduce cross-talk, not only between the pixelated photoelectric transducers but also between the Fabry-Pérot cavities.

[0055] The first step 601 illustrated in [Fig.4] and common to these variants consists of producing resin patterns 503Ai of different height, subsequently called pillars (here three pillars 503A1, 503A2 and 503A3), above the barrier layer 501, it being understood that these pillars could be produced directly on the substrate 500. To do this, we start by depositing a layer of resin which is then structured in three dimensions by Grayscale lithography using masks M1, M2 and M3 of different densities. The exposure of the resin is thus different and we obtain, after development, the three pillars 503Ai of different height, the resin between the pillars being entirely removed so that there is an empty space between each pillar 503Ai.

[0056] As in the case of Figures 1 and 2, it is appropriate to have at least two pillars 503Ai of resin of different heights (here the 3 pillars each have different heights). Among all of these pillars 503Ai, one of them, here the pillar 503A1, has a maximum height Hmax, called reference, the height being measured perpendicular to the plane of the substrate 500 along the Ox axis. More generally, the height of the pillar 503Ai will be noted hresist i. Thus, in the figure, Hmax is equal to hresist_i. Each pillar 503Ai is opposite along the Oy axis of the corresponding transducer 502Ai. As in the case of [Fig.l], the resin pillars 503i are crosslinked in order to densify them.

[0057] It will be noted that the pillars 502Ai of [Fig.4] are made of resin but that they could also be made of an organic or inorganic material by means of an underlayer such as presented with reference to [Fig.2] by transfer of resin patterns into the underlayer.

[0058] The following step 602 illustrated in [Fig. 5] is also common to these variants of the method according to the invention and corresponds to steps 103-104 and 303 of FIGS. 1 and 2. This involves either depositing an encapsulation layer then a reflective layer on the pillars 502Ai when the latter are made of resin or simply a reflective layer on the pillars 502Ai when the latter are made of organic or inorganic material. For the sake of simplification, the encapsulation layer and the reflective layer (case of resin pillars) or the reflective layer (case of the pillars of the underlayer) are represented by a single layer 505 in [Fig. 5] subsequently designated by the generic term “reflective layer”. The techniques for producing this layer are similar to those already presented with reference to FIGS. 1 and 2.The thickness of the reflective layer varies between ten nanometers and several hundred nanometers depending on the metal chosen and the design choices.

[0059] [Fig.6] illustrates steps 603 to 607 of a first variant embodiment of optical isolation between adjacent pixels (i.e. between photoelectric transducers 502Ai and between pillars 503Ai of resin or underlay material).

[0060] Step 603 consists of depositing a layer, called the insulation layer 506. This substantially flat insulation layer covers all of the pillars 503Ai covered with the reflective layer 505 and has an upper surface 507, each point of which is located at a height relative to the carrier substrate greater than the maximum reference height Hmax. As we will see later, the insulation layer 506 can be made of a sacrificial material (i.e. intended to disappear) or, on the contrary, of a material with a high optical index or low optical index intended to ensure isolation between the photoelectric transducers 502Ai.A material with a high or low optical index is understood to mean a material having an optical refractive index strictly lower or strictly higher than the refractive index of the resin or the underlayer material and the refractive index of the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities.

[0061] For materials with a high optical index, a material such as SiN can be used, and for materials with a low optical index, polymers containing fluorinated groups. We will see later that when the material used is a sacrificial material, the objective is then to create air gaps to achieve insulation.

[0062] Step 604 consists of depositing a layer of photosensitive or electrosensitive resin 508 above the insulation layer 506.

[0063] Step 605 then consists of making trenches 509 aligned with the edges of the pillars 503Ai. To do this, the photo or electrosensitive resin layer 508 is exposed using lithography equipment, in order to define on its surface a regular trench grid after development of the resin. The lithography used here is a conventional lithography. The trenches 509 are created after removal of the resin leaving resin lines 510 above the layer 506 of insulation material in the area located between each pillar 503Ai.

[0064] According to step 606, in the open spaces in the resin formed by the trenches 509, the insulation material is also etched with a stop on the reflective layer 505. At the end of this step 606, there remain on the respective edges of each pillar 503Ai borders or walls 511 of insulation material, each border 511 being extended by a line of resin 510.

[0065] The next step 607 then consists of removing (by etching or stripping technology according to the English terminology) the resin lines 510 so as to leave only the edges or walls 511 of insulating material on each side of the pillars 503Ai filling the empty space between the pillars 503Ai. The walls 511 can act as optical insulators between adjacent pixels. They can also act as containment walls for the resin or underlayment material pillars. The walls will also prevent deformation of the resin or underlayment material pillars during the upcoming planarization step.

[0066] [Fig.7] illustrates steps 603' to 606' of a second variant embodiment of optical isolation between adjacent pixels (i.e. between photoelectric transducers 502Ai and between patterns 503Ai of resin or underlay material).

[0067] Step 603' consists of depositing a photosensitive or electrosensitive resin layer 506'. This resin layer 506' covers all of the pillars 503Ai covered with the reflective layer 505 and has an upper surface 507' each point of which is located at a height relative to the carrier substrate greater than the maximum reference height Hmax.

[0068] Step 604' then consists of making trenches 509' creating empty spaces between each pillar 503Ai. To do this, the layer of photo or electrosensitive resin 507' is exposed using lithography equipment, in order to define on its surface a regular trench grid after resin development. The lithography used here is a conventional lithography. The 509' trenches are created after resin removal leaving 510' resin above each 503Ai pillar.

[0069] According to the following step 605', a layer, called the insulation layer 511', is deposited. This insulation layer 511' covers the entire resin 510' and fills the trenches 509' to a height strictly greater than Hmax. As in the case of [Fig.6], the insulation layer 511' can be made of a sacrificial material (i.e. intended to disappear) or on the contrary of a material with a high optical index or low optical index intended to ensure the insulation between the photoelectric transducers 502Ai.

[0070] Step 606' then consists of removing the resin 510' as well as the material of the insulation layer 511' located above the resin 510', for example by etching or stripping techniques according to the English terminology so as to leave only walls 511 of insulation material on each side of the pillars 503Ai filling the empty space between said pillars 503Ai. It can be seen that the structure obtained after steps 603' to 606' of [Fig.7] is identical to that obtained after steps 603 to 607 of [Fig.6].

[0071] Starting from the structure obtained at the end of step 607 of [Fig.6] or step 606' of [Fig.7], [Fig.8] illustrates steps 608 to 612 for producing the Fabry-Pérot cavities. It will be noted that these steps 609 to 612 are substantially the same as steps 105 to 108 and 304 to 307 of Figures 1 and 2.

[0072] Step 608 thus consists of starting from the structure obtained at the end of step 607 of [Fig.6] or step 606' of [Fig.7].

[0073] The following step 609 consists of depositing a layer 706 made of the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities. The layer 706 of dielectric material covers all of the pillars 503Ai covered with the reflective layer 505. The layer 706 has an upper surface 707 (not necessarily flat) each point of which is located at a height, relative to the carrier substrate 500, greater than the maximum reference height Hmax. The material of the layer 706 is preferably, but not limited to, a transparent material in the visible range such as an organic material of the polymer or inorganic type (oxide, silicon nitride, alumina, etc.). The deposition is preferably a conformal deposition, for example carried out by a PVD, CVD, LPCVD or PECVD deposition technique.

[0074] The method then comprises a step 610 of planarization of the layer 706 made in the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities so as to form a surface-planarized layer 708 by removal of the dielectric material from the layer 706. The planarization is carried out with a stop on the reflective layer 505 located at its highest level (i.e. at the level of the reference height of pillar 503A1).

[0075] The method according to the invention then comprises a step 611 of conformal deposition of a layer 709 of the same dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities as during step 609. The height of the layer 709 is noted hc, the height being measured perpendicular to the plane of the substrate. After this step, a plurality of dielectric patterns of Fabry-Pérot cavity 704Ai are obtained (here three patterns 704A1, 704A2 and 704A3).

[0076] For each dielectric pattern 704Ai, hdiel_i is the height of the pattern, the height being measured perpendicular to the plane of the substrate. The height hdiel_i of the pattern 704i can be determined according to the methods mentioned above. According to the method according to the invention, the height hdiel_i is fixed by the following formula: hdiel_i = Hmax -hresisti+ hc.

[0077] Thus, for pattern 704A1, hdiel_l is here directly equal to the height hc of layer 709.

[0078] More generally, for each pattern 704Ai, the height is technologically determined by the difference in height between that of the highest 503Al resin pattern Hmax and the height of the 503Ai resin pattern to which the height of the second dielectric layer 709 is added.

[0079] Step 612 of the method according to the invention then consists of depositing a second reflective layer 710, for example with a thickness of between 20 and 50 nm, covering the second dielectric layer 709 above the Fabry-Pérot cavity patterns 704Ai. This planar reflective layer 710 forms the second reflective layer of the Fabry-Pérot cavity type color filters. The reflective layer 710 is deposited conformally. We thus obtain a plurality (here 3) of filters Fi (ie Fl, F2 and F3) of colors of Fabry-Pérot cavity type each formed by the first reflective layer 505, the pattern 704Ai and the second reflective layer 710. It will be noted that at this stage, the photoelectric transducers 502Ai as well as the pillars 503Ai are well insulated by the walls 511 but that the dielectric patterns 704Ai and therefore the Fabry-Pérot cavities are not totally insulated.

[0080] [Fig.9] illustrates two variants of embodiment of an isolation aiming to reduce the cross-talk not only between the photoelectric transducers 502Ai as well as the pillars 503Ai but also between the dielectric patterns 704Ai and therefore the Fabry-Pérot cavities.

[0081] Starting from the structure obtained at the end of step 612 of [Fig.8], step 613 consists of depositing a layer of resin 711 on the second reflective layer 711.

[0082] Step 614 then consists of making trenches 712 aligned with the walls 511. To do this, the layer of photo or electrosensitive resin 711 is exposed using of lithography equipment, in order to define on its surface a regular trench grid after development of the resin. The lithography used here is a conventional lithography. The trenches 712 are created after removal of the resin leaving resin lines 713 above the second reflective layer 710 in the area located above each pillar 503Ai.

[0083] According to step 615, in the open spaces in the resin formed by the trenches 712, the metal of the second reflective layer 710 is also etched, as well as the dielectric material used for the Fabry-Pérot cavities, so as to access the walls 511.

[0084] The method can then take two different paths depending on whether the material of the walls 511 is a sacrificial material or a material with a high optical index or low optical index intended to provide optical insulation.

[0085] According to a first variant in which the material of the walls 511 is a sacrificial material, the method comprises a step 616 of removing the walls 511 so as to form air trenches 714 (“air-gap” according to the English terminology) completely isolating from each other the photoelectric transducers 502Ai, the pillars 503Ai and the dielectric patterns 704Ai and therefore the Fabry-Pérot cavities.

[0086] Step 617 finally consists of removing the remaining resin 713 by stripping or etching.

[0087] According to a second variant in which the material of the walls 511 is a material with a high or low optical index, the method comprises a step 616' of depositing a layer 714' of said material with a high or low refractive index so as to form walls made of this material completely isolating the photoelectric transducers 502Ai, the pillars 503Ai and the dielectric patterns 704Ai and therefore the Fabry-Pérot cavities.

[0088] Step 617' finally consists of removing by stripping or etching the remaining resin 713 as well as the low or high optical index material located above the resin.

[0089] Whether they are the air trenches 714 or the isolation walls 714', the latter ensure complete isolation of the entire Fabry-Pérot cavity as well as the photoelectric transducer associated with it. In addition, each resin pillar (or made from the material of the underlayer) on which the first reflective layer is deposited acts as a structure which guides the light waves transmitted from the filter to the transducer or from the transducer to the filter: such an arrangement further limits the risk of cross talk between two adjacent filters and two adjacent transducers and increases the electro-optical performances of the filters.

Claims

Claims

1. A method (100, 300) of manufacturing a multispectral filter for electromagnetic radiation, said filter comprising at least two color filters, each filter comprising a first reflective layer, a second reflective layer, a layer of Fabry-Pérot cavity dielectric material between the first reflective layer and the second reflective layer, the thickness of the dielectric layer of the two color filters being different and each of the two filters facing a photoelectric transducer, said method comprising the following steps: • Deposition on a carrier substrate comprising at least two photoelectric transducers, of a layer of structuring material; • Three-dimensional structuring (101, 102, 301, 302) of the layer of structuring material so as to obtain at least two patterns of structuring material of different heights, at least one of the patterns having a maximum reference height relative to the carrier substrate, the height being measured perpendicular to the plane of the substrate, each of the patterns being opposite a photoelectric transducer; • Conformal deposition (104, 303) of a first reflective layer on the at least two patterns of structuring material; • Deposition (105, 304) of a layer made in the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities, said layer of dielectric material covering all of the patterns by having an upper surface of which each point is located at a height greater than the maximum reference height; • Planarization (106, 305) by removal of the dielectric material with selective stopping at the top of the highest structuring material pattern covered with the reflective layer; • Deposition (107, 306) of a layer made from the same dielectric material so as to finalize the formation of the Fabry-Pérot cavities; • Deposition (108, 307) of a second reflective layer on the at least two Fabry-Pérot cavities.

2. Method (100) according to claim 1 characterized in that the structuring material is a resin, said structuring step (101, 102) being carried out by a grayscale lithography step on the layer of structuring material followed by a resin crosslinking step.

3. Method according to the preceding claim, characterized in that the structuring step is followed, before the step of conformal deposition (104) of the first reflective layer on the at least two patterns of structuring material, by a step of conformal deposition (103) of an encapsulation layer on the at least two patterns of structuring material, said first reflective layer covering the encapsulation layer.

4. Method (300) according to claim 1 characterized in that said structuring material is an organic or inorganic insulating material, said structuring step comprising the following sub-steps: - Deposition (301) of a layer of resin following the step of deposition of the layer of organic or inorganic insulating material; - Lithography (301) in gray level called Grayscale on the layer of resin so as to structure in three dimensions the layer of resin to obtain at least two resin patterns of different heights; - Transfer (302) of the two resin patterns into the layer of organic or inorganic material so as to obtain said at least two patterns of structuring material of different heights.

5. Method (100, 300) according to one of the preceding claims, characterized in that the deposition of the layer produced in the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities and the deposition of a layer produced in the same dielectric material so as to finalize the formation of the Fabry-Pérot cavities are conformal depositions.

6. Method according to one of the preceding claims, characterized in that the step of structuring (601) in three dimensions the layer of structuring material is a step of obtaining at least two patterns of structuring material of different heights having an empty space between said at least two structuring patterns.

7. Method according to the preceding claim, characterized in that it comprises, after the step of conformal deposition of the first reflective layer and before the deposition of the layer produced in the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities, the following steps: - Deposition (603) of a layer, called an insulating layer, said insulating layer covering all of the structuring material patterns by having an upper surface of which each point is located at a height relative to the carrier substrate greater than the maximum reference height; - Deposition (604) of a layer of resin above said insulation layer; - Removing (605) the resin in order to keep the resin only above the empty space(s) between the structuring material patterns and leaving the insulation layer exposed above the structuring material patterns; - Removing (606) the material of the insulation layer in the exposed area of the insulation layer; - Removing (607) the remaining resin in order to preserve walls made of said material of the insulation layer between the patterns of structuring material.

8. Method according to claim 6 characterized in that it comprises, after the step of conformal deposition of the first reflective layer and before the deposition of the layer produced in the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities, the following steps: - Deposition (603') of a layer of resin covering all of the structuring material patterns, presenting an upper surface of which each point is located at a height relative to the carrier substrate greater than the maximum reference height; - Removing (604') the resin between the structuring material patterns in order to keep the resin only above the structuring material patterns; - Deposition (605') of a layer, called an insulating layer, said insulating layer covering all of the patterns of structuring material covered with resin and filling the spaces between said patterns, presenting an upper surface of which each point is located at a height relative to the carrier substrate greater than the maximum reference height; - Removing (606') the insulation layer material located above the structuring material patterns and the remaining resin in order to maintain walls made of said insulation layer material between the structuring material patterns.

9. Method according to one of claims 7 or 8 in which said material of the insulation layer is a sacrificial material, said method being characterized in that it comprises the following steps: - Deposition (613) of a layer of resin on the second reflective layer; - Removing (614) the resin in the areas above the space(s) between the patterns of structuring material; - Removing (615, 616) the material of the second reflective layer, the dielectric material intended to form the dielectric patterns of the Fabry-Pérot cavities and the sacrificial material in the areas above the space(s) between the patterns of structuring material so as to form void walls between the patterns of structuring material and between the Fabry-Pérot cavities overhanging them; - Removal (617) of the remaining resin.

10. Method according to one of claims 7 or 8 in which said material of the insulation layer is a dielectric material with a low optical index, characterized in that it comprises the following steps: Deposition (613) of a layer of resin on the second reflective layer; Removing (614) the resin in the areas above the space(s) between the structuring material patterns; Removing (615) the material of the second reflective layer and the dielectric material in the areas not protected by the remaining resin so as to access the low optical index dielectric material; Deposition (616') of a layer of the low optical index dielectric material above the remaining resin and supplementing the dielectric material already present between the structuring material patterns so as to fill the void between the Fabry-Pérot cavities overhanging them; Removing (617') the resin and the low optical index dielectric material above the resin areas, leaving the low optical index material between the structuring material patterns and between the Fabry-Pérot cavities overlying them so as to form dielectric insulation walls.

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