Polarimetric image sensor

Abstract

Polarimetric Image Sensor This description relates to a polarimetric image sensor (100) formed in and on a semiconductor substrate (101), the sensor comprising a plurality of pixels (P) each comprising: - a photosensitive region (103) formed in the semiconductor substrate (101); - a diffraction structure (119) formed on the side of an illumination face of the photosensitive region (103); and - a polarization structure (111) formed on the side of the diffraction structure (119) opposite the photosensitive region (103). Figure for the abstract: Fig. 1

Description

Description Title of the invention: Polarimetric image sensor Technical field This description relates generally to image sensors, and more particularly to so-called polarimetric image sensors, adapted to recording information relating to the polarization of the captured light. Prior art Measuring light polarization information during image acquisition can be of interest for many applications. In particular, it allows the implementation of image enhancement treatments, adapted according to the application considered. For example, it can reduce or, on the contrary, exacerbate reflections on an image of a surface such as a window or water. It also makes it possible to detect manufactured objects in a natural environment (camouflage detection or mine clearance applications for example), the latter generally having a polarization signature.Among the applications that can benefit from the measurement of polarization information, we can also cite industrial control applications, biomedical applications, for example applications for detecting cancer cells (the latter polarizing light due to their fibrous nature), contrast enhancement applications for capturing images in a scattering environment (fog, underwater imaging, etc.), or even distance mapping applications or acquisition of depth images, in which polarization can provide information on the orientation of the surface of manufactured objects, and thus help 3D reconstruction in addition to another modality such as active illumination by structured light or by time-of-flight measurement. To measure polarization information, it has already been proposed to successively acquire, using the same sensor, several images of the same scene, by placing a polarizer opposite the sensor at each acquisition, and changing the polarizer between two successive acquisitions. This results in relatively bulky acquisition systems, with the presence in front of the sensor of a mechanism, for example a wheel or motorized rotating stage on which the different polarizers are fixed, allowing the polarizer to be changed between two acquisitions. Another limitation is linked to the need to successively acquire several images of the scene to record several polarization states. This can be particularly problematic when the scene varies over time. To overcome these limitations, it has been proposed to place a matrix of polarizing filters opposite the image sensor. A limitation remains, however, that the polarizing filters block part of the light signal received by the acquisition system. Thus, the overall sensitivity or overall quantum efficiency of the acquisition system is relatively low. It would be desirable to at least partially overcome certain limitations of known polarimetric image acquisition solutions. Summary of the invention For this, one embodiment provides a polarimetric image sensor formed in and on a semiconductor substrate, the sensor comprising a plurality of pixels each comprising: - a photosensitive region formed in the semiconductor substrate; - a diffraction structure formed on the side of an illumination face of the photosensitive region; and - a polarization structure formed on the side of the diffraction structure opposite the photosensitive region. According to one embodiment, the plurality of pixels comprises at least first and second pixels adapted to measure radiation according to respectively first and second distinct polarizations, in which: the polarization structure of the first pixel is adapted to transmit mainly radiation according to the first polarization and the polarization structure of the second pixel is adapted to transmit mainly radiation according to the second polarization; and the diffraction structure of the first pixel is adapted to promote the absorption, in the photosensitive region of the pixel, of the radiation according to the first polarization relative to the radiation according to the second polarization, and the diffraction structure of the second pixel is adapted to promote the absorption, in the photosensitive region of the pixel, of the radiation according to the second polarization relative to the radiation according to the first polarization. According to one embodiment, in each pixel, the polarization structure of the pixel comprises a plurality of parallel bars. According to one embodiment, the parallel bars are metallic. According to one embodiment, in each pixel, the diffraction structure of the pixel comprises a plurality of cavities or trenches extending vertically in the substrate on the side of the illumination face of the photosensitive region. According to one embodiment, the cavities or trenches extend to a depth of between 50 and 500 nm. According to one embodiment, the plurality of pixels comprises different pixels adapted to measure radiation in different wavelength ranges, and, in each pixel, the polarization structure and / or the diffraction structure are adapted according to the wavelength range intended to be measured by the pixel. According to one embodiment, in each pixel, the polarization structure and / or the diffraction structure are adapted according to the angle of incidence of the radiation received by the pixel. According to one embodiment, the sensor comprises an interconnect stack covering a face of the substrate opposite the diffraction structures and the polarization structures. According to one embodiment, the polarization structures are polarizing filters. According to one embodiment, the polarization structures are polarization routers. Brief description of the drawings These and other features and advantages will be set forth in detail in the following description of particular embodiments given without limitation in relation to the attached figures, among which: [Fig. 1] is a partial and schematic sectional view of an example of a polarimetric image sensor according to one embodiment; [Fig.2] is a schematic top view of an exemplary embodiment of polarization structures of the sensor of [Fig.1]; [Fig.3] is a schematic top view of an exemplary embodiment of diffraction structures of the sensor of [Fig.1]; and [Fig.4A], [Fig.4B], [Fig.4C], [Fig.4D], [Fig.4E], [Fig.4F], [Fig.4G], [Fig.4H] ​​and [Fig.41] are sectional views illustrating successive steps of an example of a method for producing the sensor of [Fig.1]. Description of the embodiments The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties. For the sake of clarity, only the steps and elements useful for understanding the embodiments described have been shown and are detailed. In particular, the photo-detection elements and the electronic control circuits of the image sensors described have not been detailed, the embodiments described being compatible with the usual embodiments of these elements. In addition, the applications that the image sensors described have not been detailed, the described embodiments being compatible with all or most known applications of polarimetric image acquisition systems. Unless otherwise specified, when referring to two elements connected together, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") together, this means that these two elements can be connected or be connected by means of one or more other elements. In the following description, when reference is made to absolute position qualifiers, such as the terms “front”, “back”, “top”, “bottom”, “left”, “right”, etc., or relative position qualifiers, such as the terms “above”, “below”, “upper”, “lower”, etc., or to orientation qualifiers, such as the terms “horizontal”, “vertical”, etc., reference is made unless otherwise specified to the orientation of the figures. Unless otherwise specified, the expressions 'about', 'approximately', 'substantially', and 'of the order of' mean to within 10%, preferably to within 5%. [Fig. 1] is a partial and schematic sectional view of an example of a polarimetric image sensor 100 according to one embodiment. The sensor 100 is formed in and on a semiconductor substrate 101. The substrate 101 is for example made of a monocrystalline semiconductor material. The substrate 101 is for example made of silicon, for example monocrystalline silicon. The sensor 100 comprises a plurality of pixels P formed in and on the semiconductor substrate 101. In top view, the pixels P are for example arranged in a matrix according to rows and columns. The sensor 100 further comprises, on the side of a first face of the substrate 101, called the front face, corresponding to the lower face of the substrate 101 in the orientation of the figure, a stack 105 of insulating and conductive layers (for example metallic), called the interconnection stack, in which interconnection elements (for example conductive interconnection tracks and vias) of the pixels of the sensor are formed. In the example of [Fig. 1], the sensor 100 is a backside illumination sensor, also called a BSI sensor (from the English “Backside Illumination Sensor”), that is to say that the light rays coming from the scene to be imaged illuminate the substrate from its backside, that is to say its side opposite the interconnection stack 105, namely its upper side in the orientation of [Fig. 1]. Each pixel P of the sensor 100 comprises a photosensitive region 103 formed in the substrate 101. Each photosensitive region 103 comprises, for example, a photo-detection element 107, for example a photodiode. In the example shown, the photosensitive regions 103 of the pixels P are laterally separated from each other. by insulating walls 109. The insulating walls 109 are for example made of a dielectric material, for example silicon oxide. As a variant (not detailed in the figures), the insulating walls 109 comprise external side walls made of a dielectric material, for example silicon oxide, and a central wall made of an electrically conductive material, for example doped polycrystalline silicon or a metal. In this example, the insulating walls 109 extend vertically through the entire thickness of the substrate 101. The thickness of the substrate 101 is for example between 1 and 20 μm, for example between 3 and 10 μm. As a variant, the insulating walls 109 can be omitted. Each pixel P comprises a polarization structure 111, for example a polarizing filter, arranged opposite the photosensitive region 103 of the pixel, on the side of the illumination face of the photosensitive region 103, that is to say on the side of the upper face of the substrate 101 in the orientation of [Fig.1]. Each polarization structure 111 is adapted to transmit mainly light radiation according to a predefined polarization. In the example of [Fig. 1], the sensor comprises several pixels P whose respective polarization structures 111 have different polarization orientations and are thus adapted to transmit mainly light rays according to different polarizations. This makes it possible to measure, by means of distinct pixels P, intensities of light radiation received according to different polarizations. In other words, the sensor comprises at least first and second pixels P intended to measure intensities of light radiation received according to first and second polarizations respectively, for example first and second orthogonal linear polarizations.By way of example, the polarization structure 111 of the first pixel has a radiation transmission coefficient according to the first polarization greater than its radiation transmission coefficient according to the second polarization, and the polarization structure 111 of the second pixel has a radiation transmission coefficient according to the second polarization greater than its radiation transmission coefficient according to the first polarization. Polarization structures are, for example, metal structures comprising openings and transmitting mainly radiation according to a predefined polarization, and absorbing or reflecting radiation according to other polarizations. Metal structures are, for example, made of aluminum or copper. Alternatively, other metals can be used, for example, silver, gold, tungsten or titanium. For example, a filler material 115, for example a dielectric material, for example silicon oxide, silicon nitride, alumina (Al, Oz), tantalum oxide or hafnium oxide, fills the openings formed in the metal structures. In this example, the material 115 further covers the polarization structures 111, forming a planarization layer 115. Alternatively, the openings of the polarization structures 111 can be left empty or filled with air. In practice, the choice of patterns and the dimensioning of the 111 polarization structures can be carried out using known electromagnetic simulation tools. For example, the pixels P are divided into macropixels M, each comprising at least two adjacent pixels P. In each macropixel M, the pixels P of the macropixel have different polarization structures 111. Thus, in each macropixel M, the pixels P of the macropixel measure intensities of light radiation received according to different polarizations. [Fig.2] schematically illustrates the polarization structures 111 of the pixels P of the same macropixel M. In this example, each macropixel M comprises four adjacent pixels P adapted to measure intensities of light radiation received according to respectively four different polarization orientations, for example linear polarizations according to respectively four directions forming respectively angles of 0°, 90°, +45° and -45° relative to a reference direction. In this example the four pixels P are arranged in a matrix according to two rows and two columns. The polarization structures are, for example, metal grids each consisting of a plurality of regularly spaced parallel metal bars, transmitting mainly the radiation according to a linear polarization perpendicular to the metal bars, and absorbing the radiation according to the other polarizations. Alternatively, the number of pixels P per macropixel M may be other than four. Furthermore, the described embodiments are not limited to linear 111 polarization structures. Alternatively, each macropixel M may comprise one or more linear 111 polarization structures and / or one or more circular 111 polarization structures. For example, the polarization structures 111 of the pixels P of the same position in the different macropixels M of the sensor are adapted to transmit mainly the same polarization orientation. For example, the polarization structures 111 of the same polarization orientation in the different macro-pixels M of the sensor are all identical, apart from manufacturing dispersions. Alternatively, the polarization structures 111 of the same polarization orientation in the different macro-pixels M of the sensor have patterns adapted in function of the position of the macropixel M on the sensor, to take into account the main direction of incidence of the light rays received by the macropixel. In the example of [Fig. 1], each pixel P of the sensor 100 comprises a color filter 113 arranged above the polarization structure and adapted to transmit light predominantly in a determined wavelength range. Different pixels P may comprise different color filters 113. For example, the sensor comprises pixels P comprising a color filter 113 adapted to transmit predominantly red light (R), pixels P comprising a color filter 113 adapted to transmit predominantly green light (G), and pixels P comprising a color filter 113 adapted to transmit predominantly blue light (B). For example, the pixels P of the same macro-pixel M comprise identical color filters 113, and the pixels P of neighboring macro-pixels M comprise different color filters. The color filters 113 are for example made of colored resin. For example, the polarization structures 111 of the same polarization orientation in the different macro-pixels M of the sensor have patterns adapted according to the color of the pixel, that is to say the range of wavelengths transmitted mainly by the color filter 113 of the pixel. As a non-limiting example, for linear polarizers of the type illustrated in [Fig.2], made of aluminum with a silicon oxide filling, and intended to operate at visible and / or infrared wavelengths, the dimensioning of the metal bars can be as follows: - for blue light with a wavelength of the order of 450 nm (and / or for light with a longer wavelength, for example infrared light), the metal bars may have a height of between 50 and 100 nm, a width of the order of 60 nm and a repetition period of the order of 180 nm; - for green light with a wavelength of the order of 530 nm (and / or for light with a longer wavelength, for example infrared light), the metal bars may have a height of between 50 and 100 nm, a width of the order of 70 nm and a repetition period of the order of 210 nm; - for red light with a wavelength of the order of 610 nm (and / or for light with a longer wavelength, for example infrared light), the metal bars may have a height of between 50 and 100 nm, a width of the order of 80 nm and a repetition period of the order of 240 nm; - for infrared light with a wavelength of around 940 nm or higher, the metal bars may have a height of between 50 and 100 nm, a width of around 90 nm and a repetition period of around 280 nm. In practice, for reasons of simplification of manufacturing processes, it is It is preferable that the height of the metal bars of the polarization structures 111 be the same in all the pixels P of the sensor. Thus, compromises can be made between the complexity of producing the polarizers 111 and their polarization filtering performance. In the example of [Fig. 1], the color filters 113 are arranged above the planarization layer 115, for example in contact, by their lower face, with the upper face of the layer 115. In the example of [Fig. 1], each pixel P of the sensor 100 further comprises a microlens 117 surmounting the polarization structure 111 of the pixel, adapted to focus the incident light in the photosensitive region 103 of the pixel. In the example shown, each microlens 117 is arranged above the color filter 113 of the pixel and is for example in contact, by its lower face, with the upper face of the color filter 113. According to one aspect of an embodiment, each pixel P of the sensor 100 further comprises a diffraction structure 119 formed on the side of the illumination face of the photosensitive region 103 of the pixel, that is to say on the side of its upper face in the orientation of [Fig. 1]. The diffraction structure is arranged between the photosensitive region 103 and the polarization structure 111, for example in contact with the upper face of the substrate 101. In the example shown, the diffraction structure comprises structures, for example cavities or trenches, formed in the substrate 101 on the side of the upper face of the photosensitive region 103 of the pixel. The structures are for example filled with a material with a refractive index different from that of the substrate material, for example silicon oxide. The structures have for example a lateral dimension of the order of λ / N, λ designating the main sensitivity wavelength of the pixel, that is to say, for example, the wavelength for which the quantum efficiency of the pixel is maximum, or the main wavelength intended to be measured by the pixel, and N being the refractive index of the substrate, for example silicon, in order to be placed in the diffraction regime. In each pixel P, the structure 119 makes it possible to diffract the light upon entering the semiconductor material of the substrate, so as to increase the length of the optical path of the rays in the photosensitive region 103 of the pixel, and thus promote the absorption, and consequently the photo-conversion, of the incident rays by the photosensitive region 103 of the pixel. For example, the diffraction structures 119 of the different pixels P of the sensor are adapted as a function of the main wavelength intended to be measured by the pixel and / or the main angle of incidence of the rays reaching the pixel (i.e. as a function of the position of the pixel in the sensor). According to one aspect of the embodiment of [Fig. 1], in each pixel P of the sensor, the diffraction structure 119 of the pixel is adapted to the polarization intended to be measured mainly by the pixel, called the polarization of the pixel, so as to promote the absorption of radiation in the photosensitive region 103 mainly according to the polarization of the pixel. In other words, the pattern of the diffraction structure 119 is chosen so that the absorption of radiation polarized according to the polarization of the pixel (defined by the polarization structure 111) is greater than the absorption of radiation according to the other polarizations. Thus, in the embodiment of [Fig.1], the pixels P comprising different polarization structures 111 comprise different diffraction structures 119. The presence of the diffraction structures 119 makes it possible, in each pixel, to improve the sensitivity to the polarization of the pixel, that is to say the quantum efficiency of the illuminated pixel according to the polarization of the pixel. The diffraction structures 119 also make it possible to increase the extinction coefficient or contrast of the pixels, that is to say, in each pixel, the ratio between the quantum efficiency of the illuminated pixel according to the polarization of the pixel and the quantum efficiency of the illuminated pixel according to the polarization orthogonal to the polarization of the pixel. The diffraction structures 119 are for example strongly asymmetric to favor the diffraction of light according to the polarization of the pixel compared to other polarizations. The choice of patterns and the dimensioning of diffraction structures 119 can be carried out using electromagnetic simulation tools. [Fig. 3] schematically illustrates an example of embodiment of the diffraction structures 119 of the pixels P of the macropixel M of [Fig. 2]. In this example, in each pixel, the polarization structure 119 consists of trenches parallel to the metal bars of the polarization structure 111 of the pixel, extending vertically in the substrate 101 from the upper face of the substrate 101. It will be noted, however, that the polarization structures 111 and the diffraction structures 119 may be different in terms of design and materials, and do not exploit the same physical principles. In particular, the role of the polarization structures 111 is to transmit mainly the main polarization of the pixel and to absorb or reflect the other polarizations, while the role of the diffraction structure 119 is to diffract the main polarization of the pixel more strongly compared to the other polarizations. As a result, the structures 111 and 119 of the same pixel P do not necessarily have the same main axis and their respective orientations may depend on parameters such as the wavelength, the aperture ratio and / or the size of the pixel. Thus, as a variant, not shown, each diffraction structure 119 can be made up of trenches orthogonal to the metal bars of the polarization structure 111 of the pixel. It will further be noted that the lateral dimensions and repetition period of the trenches of the diffraction structures 119 are not necessarily identical to the lateral dimensions and repetition period of the metal bars of the polarization structures 111. In addition, the depth of the trenches of the diffraction structures may be different from the height of the metal bars of the polarization structures. In the example considered above in which each macropixel M comprises several pixels P adapted to respectively measure different linear polarizations, the polarization structures 111 of the different pixels have for example the same pattern, rotated by an angle © equal to the angle formed between the polarization direction to be measured and a reference direction. Similarly, the diffraction structures 119 of the different pixels have for example the same pattern, also rotated by the angle 60. Figures 4A to 41 are sectional views illustrating successive steps of an example of a method of manufacturing the sensor 100 of [Fig. 1]. [Fig.4A] illustrates an intermediate structure at the end of a step of forming the photodetectors 107 in the substrate 101, on the lower face of the substrate, then a step of forming the interconnection stack 105 on the lower face of the substrate. Control and / or read transistors, not detailed in the figures, can also be formed in and on the lower face of the substrate, before the interconnection stack 105 is formed. In the example of [Fig.4A], after the formation of the photodetectors 107 and the interconnect stack 105, the substrate 101 is thinned by its rear face, that is to say its upper face in the orientation of [Fig.4A]. Before the thinning step, a substrate 401, serving as a support handle, is fixed, by its upper face, to the lower face of the interconnect stack 105. It will be noted that in the sectional views of FIGS. 4A to 41, the lateral isolation walls 109 of the pixels have not been shown. The walls 109 may be formed on the side of the front face of the substrate 101, before the formation of the interconnection stack 105, or by the rear face of the substrate 101, after the step of thinning the substrate. [Fig.4B] illustrates the structure obtained at the end of a step of etching trenches located in the substrate 101, on the side of the rear face of the substrate 101, to form the diffraction structures 119 of the pixels. The trenches etched in this step have, for example, a depth of between 50 and 500 nm. [Fig.4C] illustrates the structure obtained at the end of a step of depositing a passivation layer 403, for example made of a dielectric material, on and in contact with the upper face of the substrate 102 at the end of the etching step of [Fig.4B]. The layer 403 is for example deposited continuously and with a substantially uniform thickness over the entire upper surface of the structure of [Fig.4B]. The layer 403 is for example deposited by a conformal deposition method. The thickness of the layer 403 is for example relatively small so that the layer 403 does not completely fill the trenches. For example, the thickness of the layer 403 is between 1 and 20 nm, for example between 1 and 10 nm. The layer 403 is for example made of an electrically charged oxide, for example alumina (Al,O3) or hafnium oxide (HfO-). [Fig.4D] illustrates the structure obtained at the end of a step of depositing a planarization layer 405 filling the trenches of the diffraction structures 119 and covering the diffraction structures 119. In this example, the layer 405 has a substantially planar upper face extending over the entire surface of the sensor. The layer 405 is for example made of silicon oxide or silicon nitride. [Fig.4E] illustrates the structure obtained at the end of a step of depositing an optional transparent layer 407 acting as an optical spacer, on the upper face of the layer 405. The layer 407 is for example made of a transparent material with a relatively low refractive index, for example less than 2. [Fig.4F] illustrates the structure obtained at the end of a step of forming the polarization structures 111 of the sensor, for example made of metal, on the upper face of the layer 407. By way of example, a metal layer, for example made of aluminum, is first deposited continuously and with a uniform thickness over the entire upper surface of the structure, then removed in a localized manner, for example by photolithography and etching, to define the polarizers 111. [Fig.4G] illustrates the structure obtained at the end of a step of depositing the transparent planarization layer 115 filling the openings of the polarizers 111 and covering the polarizers 111. [Fig.4H] ​​illustrates the structure obtained at the end of a step of forming the colored filters 113, for example in resin, on the upper face of the structure of [Fig.4G]. [Fig.41] illustrates the structure obtained at the end of a step of forming microlenses 117 on the upper face of the structure of [Fig.4H]. Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art. In particular, although exemplary embodiments of backside illumination (BSI) sensors have been described above, the described embodiments may be adapted to frontside illumination (FSI) sensors. "Front Side Illumination"). In this case, the photosensitive region of each pixel is illuminated through the interconnect stack 105. The diffraction structures 119 are then formed on the front side (bottom side in the orientation of [Fig. 1]) of the substrate, before the formation of the interconnect stack 105. For example, the diffraction structures may then be trenches similar to what was described above, but etched on the front side of the substrate. Alternatively, the diffraction structures may be formed by polycrystalline silicon pads or rods formed on the front side of the substrate. For example, the diffraction structures may be formed in the same level of polycrystalline silicon as that used to form conductive gates of MOS transistors of the sensor pixels.This has the advantage of not requiring etching of the substrate 101 to form the diffraction structures 119. Furthermore, in the case of a front-facing illumination sensor, the polarization structures 111 may be formed in one or more metal levels of the interconnection stack 105. Here again, this makes it possible not to introduce an additional step for the manufacture of the polarization structures 111. Furthermore, the embodiments described are not limited to the examples presented above of producing polarization structures 111 consisting of opaque metal patterns, laterally surrounded by a transparent dielectric material. As a variant, the polarization structures 111 may be produced based on transparent or semi-transparent materials having an index contrast, so as to improve the transmission of the polarizers. For example, for polarization structures intended to operate in the near infrared, for example at a wavelength of the order of 940 nm, it is possible to use silicon patterns, for example amorphous silicon, surrounded by a dielectric material with a lower refractive index, for example silicon oxide.For pixels intended to measure visible radiation, it is possible to use patterns made of silicon nitride or titanium oxide, surrounded by a dielectric material with a lower refractive index, for example silicon oxide. Furthermore, examples of polarizing structures 111 consisting of parallel bars of orientation chosen according to the linear polarization direction to be transmitted have been described above. These are sub-wavelength structures that can be described as one-dimensional (1D) metasurfaces because they are structured along a single axis. Alternatively, the polarizing structures 111 can be made based on two-dimensional (2D) metasurfaces, consisting of pillars or pads arranged in the form of a two-dimensional network. To obtain the desired polarizing effect, pillars will be chosen which, when viewed from above, have an elongated shape, for example a rectangle or an ellipse, in a direction chosen according to the polarization direction. linearization to be transmitted. Furthermore, it will be noted that, in the examples described above, the polarization structures 111 have a polarization filtering function. In other words, the polarization that one wishes to measure is transmitted by the structure 111, while the orthogonal polarization is absorbed or reflected. This leads to a loss of luminous flux of the order of 50% in the case of depolarized light. As a variant, the polarization structures 111 may be sorting structures, adapted to deflect the light differently depending on its polarization. In particular, it will be possible to provide structures 111 adapted to deflect the light towards respectively two neighboring photosensitive regions 103 for two orthogonal polarizations. For example, in the case of a macropixel M of the type described in relation to [Fig.2], the polarization structures 111 of the four pixels P of the macropixel can be replaced by a single structure 111 extending over the entire surface of the macropixel, adapted to deflect the light towards respectively the photosensitive regions 103 of the four pixels P for the four polarizations (0°, 90°, +45° and -45°) that one seeks to measure. Such polarization sorting structures, also called polarization routers, can be realized based on two-dimensional (2D) or three-dimensional (3D) metasurfaces. The shape and sizing of the metasurface patterns can be determined using electromagnetic simulation tools, for example, by using inverse design methods, for example of the type described in the article “Multifunctional volumetric meta-optics for color and polarization image sensors” by Philip Camayd-Munoz et al. (Vol. 7, No. 4 / April 2020 / Optica) or in the article “Empowering Metasurfaces with Inverse Design: Principles and Applications” by Zhaoyi Li et al. (https: / / doi.org / 10.1021 / acsphotonics.1c01850). It will further be noted that, in a rear-facing illumination sensor of the type described in relation to [Fig. 1], depending on the thickness of the substrate 101 and the wavelength intended to be measured by the pixels, a portion of the incident light radiation may pass through the entire thickness of the substrate and be reflected on metal tracks of the interconnection stack 105, before being absorbed in the photosensitive region 103 of the pixels. The reflection on the metal tracks of the interconnection stack can lead to at least partially polarizing the light in a direction depending on the orientation of said metal tracks. Preferably, for each pixel P of the sensor, the metal tracks of the interconnection stack 105 located opposite the pixel are oriented in a direction chosen as a function of the polarization of the pixel, for example so as to promote the polarization of the reflected light according to the polarization orientation intended to be measured by the pixel. Thus, preferably, the metal tracks of the interconnection stack 105 located opposite pixels intended to measure different polarizations, have different orientations. Furthermore, the described embodiments are not limited to the application examples described above for visible or near infrared sensors. Other wavelength ranges may benefit from polarizing pixels. For example, the described embodiments may be adapted to infrared sensors intended to measure radiation with a wavelength between 1 and 2 μm, for example based on InGaAs or germanium. Finally, the practical implementation of the embodiments and variants described is within the reach of the person skilled in the art from the functional indications given above. In particular, the person skilled in the art will know, from the indications of the present description, how to design, dimension and produce the polarization structures and the diffraction structures of the pixels of the sensor, so that these structures cooperate to obtain the desired effect of improving the compromise between the sensitivity and the polarization extinction coefficient of the pixels.

Claims

Claims

1. Polarimetric image sensor (100) formed in ct on a sc- substrate semiconductor (101), the sensor comprising a plurality of pixels (P) each including: - a photosensitive region (103) formed in the semiconductor substrate (101); - a diffraction structure (119) formed on the side of one face illumination of the photosensitive region (103); and - a polarization structure (111) formed on the side of the structure of diffraction (119) opposite the photosensitive region (103).

2. The sensor (100) of claim 1, wherein said plurality of pixels (P) comprises at least first and second pixels adapted to measure radiation according to first and second respectively second distinct polarizations, in which: the polarization structure (111) of the first pixel (P) is adapted to transmit mainly radiation according to the first polarity rization and the polarization structure (111) of the second pixel (P) is adapted to transmit mainly radiation according to the second polarization; and the diffraction structure (119) of the first pixel (P) is adapted to promote the absorption, in the photosensitive region (103) of the pixel, of radiation according to the first polarization with respect to the radiation according to the second polarization, and the dif- structure fraction (119) of the second pixel (P) is adapted to favor the absorption, in the photosensitive region (103) of the pixel, of radiation according to the second polarization with respect to the radiation according to the first polarization.

3. The sensor (100) of claim 1 or 2, wherein, in each pixel (P), the polarization structure (111) of the pixel comprises a plurality of parallel bars.

4. The sensor (100) of claim 3, wherein said bars pa- The rails are metallic.

5. Sensor (100) according to any one of claims 1 to 4, in which, in each pixel (P), the diffraction structure (119) of the pixel comprises a plurality of vertically extending cavities or trenches in the substrate on the side of the illumination face of the photo- region sensitive (103).

6. The sensor (100) of claim 5, wherein said cavities or trenches extend to a depth of between 50 and 500 nm.

7. A sensor (100) according to any one of claims 1 to 6, in wherein said plurality of pixels (P) comprises different pixels adapted to measure radiation in dif- wavelength ranges different, and in which, in each pixel, the polarization structure (111) and / or the diffraction structure (119) are adapted according to the wavelength range to be measured by the pixel.

8. A sensor (100) according to any one of claims 1 to 7, in which, in each pixel (P), the polarization structure (111) and / or the diffraction structure (119) are adapted according to the angle incidence of the radiation received by the pixel.

9. Sensor (100) according to any one of claims | to 8, comprising an interconnect stack covering one face of the substrate (101) opposite the diffraction structures (119) and the polarization structures (111).

10. A sensor (100) according to any one of claims 1 to 9, in wherein the polarizing structures (111) are polarizing filters.

11. Sensor (100) according to any one of claims 1 to 9, in which the polarization structures (111) are pola- routers rization.