imaging device for acquiring a visible image and an infrared image

Abstract

The invention relates to an imaging device for acquiring visible and infrared images, comprising a visible matrix sensor (10), an infrared matrix sensor (20), and a readout integrated circuit (40, 50) superimposed on the visible matrix sensor (10) and the infrared matrix sensor (20) and formed of a readout stack (40) comprising electronic elements (42) and an interconnection stack (50). The readout stack (40) is located between the sensitive layers (12, 22) of the matrix sensors (10, 20), and the interconnection stack (50) is located on the rear face of the infrared matrix sensor (20). In addition, conductive vias (32, 33, 34) electrically connect, respectively, the interconnect stack (50) to electronic elements (14) of the visible matrix sensor (10), to electronic elements (42) of the read stack (40), and to electronic elements (23) of the infrared matrix sensor (20). Figure for the abstract: Fig. 1

Description

Title of the invention: imaging device for acquiring a visible image and an infrared image Technical field

[0001] The field of the invention is that of imaging devices adapted to acquire a visible image and an infrared image of the same scene. Imaging devices of this type make it possible in particular to reconstruct, in addition to a visible image of the scene (in grayscale or in color), depth information of this same scene. STATE OF THE PRIOR ART

[0002] There are imaging devices that allow the acquisition, simultaneously or successively, of a visible image and an infrared image of the same scene. The visible image corresponds to a two-dimensional image of the scene, which can be in grayscale or RGB (Red Green Blue) colors, while the infrared image can allow the reconstruction of a depth map of the scene. For this, the imaging devices comprise a visible matrix sensor and an infrared matrix sensor, which can be superimposed on each other, so that they have substantially the same optical alignment and allow the size to be reduced. The visible and infrared matrix sensors can then be integrated monolithically on a reading substrate which comprises a CMOS type reading integrated circuit.

[0003] Thus, documents EP 3 503 192 A1 and US 2021 / 305206 A1 describe examples of such an imaging device where the visible matrix sensor and the infrared matrix sensor are superimposed on each other while being assembled to a reading substrate.

[0004] In these examples, the visible matrix sensor comprises a sensitive layer where visible detection pixels are formed, as well as an interconnection stack electrically connected to electronic elements (transistors, diodes, etc.) of the visible detection pixels. Similarly, the infrared matrix sensor comprises a sensitive layer where infrared detection pixels are formed, as well as an interconnection stack electrically connected to the photodiodes of the infrared detection pixels. The entire infrared matrix sensor is located on the rear face of the visible matrix sensor. Finally, the reading substrate comprises a CMOS-type reading integrated circuit, assembled on the rear face of the infrared matrix sensor.

[0005] However, there is a need to improve certain aspects of such imaging devices, whether at the level of the structural configuration and / or the method of fa- brication. Statement of the invention

[0006] The invention aims to remedy at least in part the drawbacks of the prior art, and for this, to propose an imaging device suitable for acquiring a visible image and an infrared image, comprising: - a visible matrix sensor, comprising a first sensitive layer in which visible detection pixels comprising at least one electronic element are defined; - an infrared matrix sensor, comprising a second sensitive layer, superimposed on the first sensitive layer, in which infrared detection pixels are defined comprising at least one electronic element; - an integrated reading circuit, superimposed on the visible matrix sensor and the infrared matrix sensor, formed of a reading stack comprising electronic elements and an interconnection stack.

[0007] According to the invention, the reading stack is located between the first sensitive layer and the second sensitive layer, and the interconnection stack is located on the rear face of the infrared matrix sensor.

[0008] In addition, conductive vias electrically connect, respectively, the interconnect stack to the electronic elements of the visible matrix sensor, to the electronic elements of the read stack, and to the electronic elements of the infrared matrix sensor.

[0009] Some preferred but non-limiting aspects of this imaging device are as follows.

[0010] The visible matrix sensor may comprise a first insulating layer located under the first sensitive layer, and the reading stack may comprise a second insulating layer located above the electronic elements of the reading stack, the first insulating layer and the second insulating layer being in contact with each other.

[0011] The reading stack may comprise a third insulating layer located under the electronic elements of the reading stack, and the infrared matrix sensor may comprise a fourth insulating layer located above the second sensitive layer, the third insulating layer and the fourth insulating layer being in contact with each other.

[0012] Conductive vias may extend directly from the electronic elements of the infrared array sensor to conductive portions of the interconnect stack.

[0013] Conductive vias may extend directly from the electronic elements of the read stack to conductive portions of the interconnect stack.

[0014] Conductive vias may extend directly from the electronic elements of the visible matrix sensor to conductive portions of the interconnect stack.

[0015] Conductive vias may extend directly from conductive portions of the read stack, which are in electrical contact with the electronic elements of the visible matrix sensor, to conductive portions of the interconnect stack.

[0016] The second sensitive layer may be a layer structured in a plane parallel to the plane of the infrared matrix sensor forming a plurality of portions of second sensitive layer, distinct from each other in the parallel plane, so that the conductive vias electrically connecting, respectively, the interconnection stack on the one hand to the electronic elements of the visible matrix sensor and to the electronic elements of the reading stack on the other hand, do not pass through the second sensitive layer.

[0017] The second sensitive layer may be a layer structured in a plane parallel to the plane of the infrared matrix sensor forming a plurality of portions of second sensitive layer connected two by two by a connection portion of lesser thickness, so that the conductive vias electrically connecting, respectively, the interconnection stack on the one hand to the electronic elements of the visible matrix sensor and to the electronic elements of the reading stack on the other hand, pass through the connection portions.

[0018] The read stack and the interconnect stack may be first read and interconnect stacks of a first read integrated circuit, and a second read integrated circuit, formed from second read and interconnect stacks, may be assembled to the first read integrated circuit, the second interconnect stack being assembled and connected to the backside of the first interconnect stack.

[0019] The imaging device may comprise a reflective layer, located between the infrared matrix sensor and the interconnect stack, adapted to reflect incident infrared radiation intended to be detected by the infrared matrix sensor.

[0020] The reflective layer can form, with the infrared matrix sensor, the reading stack and an insulating layer located between the first sensitive layer and the reading stack, an optical cavity resonant at the wavelength of the infrared radiation.

[0021] The invention also relates to a method of manufacturing an imaging device. according to any of the preceding characteristics, comprising the following steps: - production of the visible matrix sensor, a first insulating layer covering the first sensitive layer where the electronic elements are exposed; - production of a first structure intended to form the reading stack, comprising a second insulating layer, by molecular bonding of the second insulating layer on the first insulating layer, then production of the reading stack; - production of a second structure intended to form the infrared matrix sensor, comprising a fourth insulating layer, by molecular bonding of the fourth insulating layer onto a third insulating layer of the reading stack, then production of the infrared matrix sensor; - realization of the interconnection stack from the rear face of the infrared matrix sensor.

[0022] During the step of producing the electronic elements of the reading stack, a temperature increase to a temperature at least equal to 1000°C can be carried out.

[0023] The step of producing the electronic elements of the infrared matrix sensor can be carried out after the step of producing the electronic elements of the reading stack. Brief description of the drawings

[0024] Other aspects, aims, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the appended drawings in which:

[0025] [Fig.l] is a schematic and partial view, in cross-section, of an imaging device according to one embodiment;

[0026] Figures 2A to 2H illustrate different steps of a method of manufacturing an imaging device identical or similar to that of [Fig.l];

[0027] [Fig.3A] is a schematic and partial view, in cross-section, of a imaging device according to an alternative embodiment;

[0028] [Fig.3B] is a schematic and partial view, in cross-section, of an imaging device according to an alternative embodiment similar to that of [Fig.3A];

[0029] [Fig.4] is a schematic and partial view, in cross-section, of an imaging device according to an alternative embodiment;

[0030] [Fig.5] is a schematic and partial view, in cross-section, of a device imager according to an alternative embodiment.

[0031] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0032] In the figures and in the remainder of the description, the same references represent identical or similar elements. Furthermore, the different elements are not shown to scale so as to favor the clarity of the figures. Furthermore, the different embodiments and variants are not mutually exclusive and can be combined with each other. Unless otherwise indicated, the terms "substantially", "approximately", "of the order of" mean to within 10%, and preferably to within 5%. Furthermore, the terms "between ... and ..." and equivalent mean that the limits are included, unless otherwise indicated.

[0033] [Fig.l] is a schematic and partial view, in cross-section, of an imaging device 1 according to one embodiment. It is adapted to acquire a visible image and an infrared image of the same scene, simultaneously or sequentially. In this example, the same infrared detection pixel extends opposite several adjacent visible detection pixels. Alternatively, the same infrared detection pixel may extend opposite only a single visible detection pixel.

[0034] Here and for the remainder of the description, a direct three-dimensional orthogonal XYZ reference frame is defined, where the XY plane is substantially parallel to the main plane of a support substrate 31, and where the Z axis is oriented in the direction of the matrix sensors 10, 20. In the remainder of the description, the terms “lower” and “upper” are understood as relating to an increasing positioning when moving away from the support substrate 31 in the +Z direction. Furthermore, the terms “front face” and “rear face” of an element or a layer respectively designate the face oriented towards the scene to be imaged and the face opposite the scene.

[0035] Generally speaking, the imaging device 1 comprises a vertical superposition (along the Z axis) of a visible matrix sensor 10 for acquiring the visible image, of an infrared matrix sensor 20 for acquiring the infrared image, and of an integrated reading circuit 40, 50 of CMOS type electrically connected to the visible matrix sensors 10 and infrared 20. These three elements are assembled together in a monolithic manner.

[0036] As described in detail below, the integrated reading circuit 40, 50 is formed of a reading stack 40 and an interconnection stack 50. The reading stack 40 is located between a sensitive layer 12 of the visible matrix sensor 10 and a sensitive layer 22 of the infrared matrix sensor 20. On the other hand, the interconnection stack 50 is located on the rear face of the infrared matrix sensor 20, here between the latter and a support substrate 31. Conductive vias 32 provide an electrical connection, direct or indirect, between the electronic elements 14 of the visible matrix sensor 10 and the interconnection stack 50; the conductive vias 34 provide the electrical connection between the electronic elements 23 of the infrared matrix sensor 20 and the interconnection stack 50; and the conductive vias 33 provide an electrical connection between the electronic elements 42 of the reading stack 40 and the interconnection stack 50.

[0037] By electronic element of the visible 10 and infrared 20 matrix sensors, is meant here a doped portion of a semiconductor layer which has or participates in a function of collecting or storing photogenerated electrical charges. It can thus be, among other things, a doped portion for collecting minority charge carriers of a photodetector such as a photodiode; a doped portion for temporary storage of photogenerated charges coming from a photodiode, such as a reading node (Sensing Node or Floating Diffusion, in English); a doped portion of a transfer transistor (Transfer Gate, in English) which ensures the transfer of the photogenerated charges from the photodiode to the reading node.

[0038] By electronic element of the reading stack 40, we mean here a doped portion of a semiconductor layer which participates in the processing of electrical information from the visible 10 and infrared 20 matrix sensors. It can thus be, among other things, a doped portion of a diode, a transistor, among others.

[0039] The visible matrix sensor 10 is adapted to acquire a visible image of the scene. For this purpose, it comprises a plurality of detection pixels, each adapted to receive and detect visible light radiation, these detection pixels being formed in a sensitive layer 12 adapted to absorb the visible light radiation to be detected.

[0040] The sensitive layer 12 is made from a semiconductor material, preferably doped, which is chosen to absorb the visible light radiation of interest. For example, the sensitive layer 12 may be made of monocrystalline silicon. It may have a thickness of between 2 and 10 μm, for example of the order of 4 μm. The sensitive layer 12 is formed here from a layer made of the same material in terms of chemical elements, but it may be formed from a stack of sub-layers made of different materials.

[0041] Each visible detection pixel corresponds to a part of the sensitive layer 12 in the XY plane, and comprises a photodiode 13 as well as at least one electronic element 14, for example a reading node (sensing node or floating diffusion, in English) which receives the photogenerated charges transmitted by a transfer transistor (transfer gate, in English, not shown in the figures). Such a reading node 14 acts as a temporary charge accumulator. The transfer transistor makes it possible to activate the transfer of the photogenerated charge carriers from the photodiode 13 to the reading node 14. The photodiode 13 and the reading node 14 are located in the sensitive layer 12 and are flush with its rear face. The transfer transistor may be located in the lower insulating layer 16 and also be flush with the rear face of the layer sensitive layer 12. It is in electrical contact with the photodiode 13 and the reading node 14.

[0042] The detection pixels are separated from each other, in the XY plane, by isolation structures 15 which extend vertically through the sensitive layer 12, preferably over its entire thickness. These isolation structures 15 may be deep isolation trenches of the DTI type (for Deep Trench Isolation, in English) made entirely of an electrically insulating material. They may also be capacitive deep isolation trenches (CDTI, for Capacitive Deep Trench Isolation, in English), and be formed of a core of an electrically conductive material, for example doped polycrystalline silicon, surrounded by a sheath of an electrically insulating material, for example silicon oxide.These CDTI type structures 15 can then be electrically connected to the reading circuit and provide optical isolation of the visible detection pixels from each other, and prevent the diffusion of photogenerated charge carriers from one visible detection pixel to another.

[0043] An upper insulating layer 11 extends here over and in contact with the front face of the sensitive layer 12. This insulating layer is made of an electrically insulating material such as silicon oxide or silicon nitride for example. It may completely cover the sensitive layer 12. One or more layers may also be present, which provide optical functions such as an anti-reflection function.

[0044] The imaging device 1 may comprise an optical structure having one or more optical functions, for example here filtering and focusing. Thus, in this example, each visible detection pixel is coated with a color filter 61, different from one pixel to another, so that the visible image acquired by the visible matrix sensor 10 is a color image, for example of the RGB type. The color filters 61 may be colored resin filters, and are located above the corresponding sensitive layer parts 12. They are adapted to filter the wavelengths outside the visible spectral range of interest, while transmitting here the wavelengths in the infrared. Of course, the color filters 61 may be absent, the visible image then being a monochromatic image in grayscale. Furthermore, each visible detection pixel is here coated with a microlens 62, located above the color filters 61 if applicable.The microlenses 62 are adapted to focus the incident radiation towards the photodiode 13.

[0045] The infrared matrix sensor 20 is adapted to acquire an infrared image of the scene. For this purpose, it comprises a plurality of detection pixels, each adapted to receive and detect infrared light radiation, these detection pixels being formed in a sensitive layer 22, continuous or not in the XY plane, adapted to absorb and detect infrared light radiation.

[0046] The sensitive layer 22 is for example made of a semiconductor material, preferably doped, making it possible to absorb the infrared light radiation of interest. The sensitive layer 22 can obviously be formed from a stack of sub-layers. For example, the sensitive layer 22 is made from a group IV element or semiconductor compound (column IV of the periodic table), for example germanium or a silicon and germanium compound (SiGe), or from a III-V compound, for example InGaAs, InGaAsP, or others. It can also be semiconductor materials based on quantum dots (also called quantum film or quantum dots) or multi-quantum well (QWIP) materials, or even superlattice type materials. It can have a thickness that depends on the central wavelength of the infrared spectral range, for example a thickness between 50 nm and 100 m.

[0047] Each infrared detection pixel corresponds to a part of the sensitive layer 22 in the XY plane, and comprises at least one photodetector 23 allowing the photogeneration of charge carriers, such as, for example, a photodiode (as shown in [Fig.l]). In this example, each photodiode 23 is connected directly to the integrated reading circuit 40, 50. However, electronic elements such as transistors may also be present between the photodiode 23 and the reading circuit 40, 50. The photodiode 23 is located in the sensitive layer 22 and is flush with its rear face. In this example, the electronic element 23 of the infrared detection pixel corresponds to the photodiode, but it could also be an electronic element for extracting charges (transfer transistor, reading node, etc.).

[0048] In this example, the infrared detection pixels are located opposite (perpendicular to) the visible detection pixels. The dimensions of the infrared detection pixels in the XY plane are here larger than those of the visible detection pixels, but alternatively they could be of the same order. Here, each infrared detection pixel extends opposite 2x2 visible detection pixels, being aligned with the center of the surface formed by the 2x2 visible detection pixels.

[0049] Furthermore, at least one upper insulating layer 21, made of an electrically insulating material, covers the sensitive layer 22 and has a flat front face. This is a bonding layer used to ensure molecular bonding of the infrared matrix sensor to the rear face of the reading stack 40. In addition, at least one lower insulating layer 24, made of an electrically insulating material, extends under the sensitive layer 22 and preferably has a flat rear face.

[0050] Furthermore, the imaging device 1 preferably comprises a reflective layer 63, which extends in the XY plane under the visible detection pixels and the infrared detection pixels, to ensure reflection of the incident light radiation at detect. It can be made of a metallic material, for example Ti, Al, Cu and their alloys, or heavily doped silicon, for example of the order of 1020 cm 3. It can have a thickness of the order of 400 nm when made of silicon. It can also be a multi-layer dielectric stack of the Bragg mirror type.

[0051] Note that the infrared matrix sensor 20 may be of the resonant cavity type, as described in particular in patent application FR3130450A1. Thus, the sensitive layer 22 may be a layer of low thickness, for example of the order of 500nm or even less. The sensitive layer 22 is located in a resonant optical cavity delimited vertically by the reflective layer 63 and an assembly formed by the lower insulating bonding layer 16, the reading stack 40, and the upper insulating bonding layer 21. This assembly preferably has a thickness of the order of a few hundred nanometers. The insulating layers of this assembly are preferably made of silicon oxide. Such a configuration makes it possible to obtain an absorption of infrared radiation greater than 80% in the sensitive layer 22.

[0052] The readout integrated circuit (ROIC) 40, 50 comprises a read stack 40 and an interconnect stack 50, here superimposed along the Z axis and spaced apart from each other.

[0053] The reading stack 40 is a FEOL (Front End Of Line) type stack. It is formed of semiconductor-based layers where electronic elements 42 (diodes, transistors, etc.) and possibly passive elements (capacitors, resistors, etc.) are made. The electronic elements are connected to the electronic elements of the detection pixels of the visible 10 and infrared 20 matrix sensors on the one hand, and to at least one external connection pad on the other hand (not shown), the latter being intended to connect the detection device to an external electronic device.

[0054] According to the invention, the reading stack 40 is located vertically (along the Z axis) between the sensitive layer 12 of the visible matrix sensor 10 and the sensitive layer 22 of the infrared matrix sensor 20. In addition, it is assembled by molecular bonding to the rear face of the visible matrix sensor 10.

[0055] The reading stack 40 thus comprises an upper insulating layer 41, made of an electrically insulating material, for example here of a silicon oxide. It forms a molecular bonding layer by which the reading stack 40 is assembled by molecular bonding to the insulating layer 16 of the visible matrix sensor 10. The reading stack 40 comprises electronic elements 42, covered by at least one main insulating layer 43 which has a flat lower face. This insulating layer 43 is made of an electrically insulating material insulator, for example here made of a silicon oxide, and forms a molecular bonding layer for the assembly of the infrared matrix sensor 20 on the rear face.

[0056] Furthermore, the interconnection stack 50 is a BEOL (Back End Of Line) type stack. It is formed of layers where metallization levels are defined, which are separated vertically by inter-metal dielectric layers 55 (IMD for Inter Metal Dielectric), and are connected to each other by conductive vias 54.

[0057] The interconnection levels are each formed of coplanar conductive portions 51, 52, 53, these being connected to those of the adjacent interconnection levels by the conductive vias 54. The interconnection structure therefore comprises several parallel interconnection levels arranged vertically to each other. It thus comprises a first interconnection level 51, called upper, and located on the side of the infrared matrix sensor 20, intermediate interconnection levels 52, and a last interconnection level 53, called lower, and located on the side of the support substrate 31.

[0058] The interconnection stack 50 is located under the infrared matrix sensor 20, here between the latter and the support substrate 31, and is therefore spaced from the reading stack 40 by the infrared matrix sensor 20. Furthermore, as indicated previously, conductive vias 32, 34, 33 respectively provide an electrical connection, direct or indirect, between, on the one hand, the electronic elements 14 of the visible matrix sensor 10, those 23 of the infrared matrix sensor 20, and those 42 of the reading stack 40, and on the other hand, the interconnection stack 50.

[0059] More precisely, at least one conductive via 34 provides an electrical connection, here direct, between the photodetector 23 of each infrared detection pixel and a conductive portion 51 of the upper metallization level. By direct electrical connection, it is meant here that the same conductive via extends between the two elements in question, here between the photodiode and the conductive portion. This conductive via 34 thus passes through the lower insulating layer 24, the reflective layer 63 (through an opening electrically insulated from the layer 63) and the lower insulating layer 64.

[0060] In addition, conductive vias 33 provide the electrical connection, also direct here, between the electronic elements 42 of the reading stack 40 and the conductive portions 51 of the upper metallization level. These conductive vias 33 thus pass through the main insulating layer 43, the insulating bonding layer 21, the sensitive layer 22 in this example (but the sensitive layer 22 could be structured, as described in [Fig. 3B]), the lower insulating layer 24, the reflective layer 63 (through an opening electrically insulated from the layer 63) and the lower insulating layer 64. Note that the conductive vias 33 pass through the sensitive layer 22 without electrical contact, since the conductive material of the vias 33 is surrounded by a sheath made of an electrically insulating material.

[0061] Finally, conductive vias 32 provide the electrical connection, also direct here, between the electronic elements 14 of the visible detection pixels and the conductive portions 51 of the upper metallization level. These conductive vias 32 thus pass through the two bonding layers 16, 21, the main insulating layer 43, the bonding insulating layer 21, the sensitive layer 22 in this example, the lower insulating layer 24, the reflective layer 63 (through an opening electrically insulated from the layer 63) and the lower insulating layer 64. Note here also that the conductive vias 32 pass through the sensitive layer 22 without electrical contact, insofar as the conductive material of the vias 32 is surrounded by a sheath made of an electrically insulating material.

[0062] Thus, the imaging device 1 has a structural configuration with four superimposed stages, which are successively formed from the visible matrix sensor 10, the reading stack 40, the infrared matrix sensor 20, and finally the interconnection stack 50 of the integrated reading circuit. This structural configuration is achieved by means of two molecular bonding steps, namely the bonding of the reading stack 40 on the rear face of the visible matrix sensor 10, then the bonding of the infrared matrix sensor 20 on the rear face of the reading stack 40. Also, this makes it possible to reduce the integration and implementation constraints of the method, in particular in terms of thermal budget.Indeed, by producing the reading stack 40 independently and beforehand from that of the infrared matrix sensor 20, the thermal budget associated with the production of the electronic elements 42 (control transistors in particular), and in particular the high temperatures used (around 1000°C) do not affect the quality of the sensitive layer 22 (for example in Ge, SiGe, InGaAs, etc.) of the infrared matrix sensor 20.

[0063] A method of manufacturing such an imaging device 1 is now described with reference to FIGS. 2A to 2H. In this example, the imaging device is identical to that of [Fig.l].

[0064] With reference to [Fig.2A], a structure is produced formed of a continuous layer (sensitive layer 12) of monocrystalline silicon, resting on an oxide layer 11 then on a handle layer 71 (here a thick layer of silicon). This structure is produced from a first silicon-on-insulator (SOI) substrate. The insulation structures 15 are produced, and the photodiodes 13 and the electronic elements 14 are produced by localized doping in the rear face of the sensitive layer 12. The insulating layer 16, here made of a silicon oxide, is deposited so as to passivate the rear face of the sensitive layer 12 and to form a molecular bonding layer. This layer 16 may be a multilayer, formed by example of a sub-layer ensuring passivation and a sub-layer ensuring molecular bonding. This structure thus forms the visible matrix sensor 10.

[0065] With reference to [Fig.2B], an SOI substrate is produced formed from a thick support layer 71 of silicon, a buried oxide layer 72, a thin layer 73 of monocrystalline silicon. The SOI substrate comprises an insulating bonding layer 41, made of a silicon oxide, which covers the thin silicon layer 73. It is assembled to the rear face of the visible matrix sensor 10, here by oxide / oxide molecular bonding, by bringing the bonding layers 41, 16 into mutual contact.

[0066] With reference to [Fig.2C], the reading stack 40 is produced. For this, the thick layer 71 is removed. Then the electronic elements 42 are produced using in particular the thin layers of silicon and oxide. Finally, the main insulating layer 43 is produced so as to cover the electronic elements and to have a flat rear face.

[0067] With reference to [Fig.2D], a structure is produced formed of a support layer 74, the sensitive layer 22, and an insulating layer 21, here made of a silicon oxide, which ensures the passivation of the sensitive layer 22 and the molecular bonding here of the oxide / oxide type with the main insulating layer 43. The insulating layer 21 can obviously be a multilayer, for example formed of a sub-layer ensuring the passivation and a sub-layer ensuring the molecular bonding. This structure is assembled to the rear face of the reading stack 40, here by oxide / oxide molecular bonding, by bringing the insulating layer 21 into contact with the main insulating layer 43.

[0068] With reference to [Fig.2E], the infrared matrix sensor 20 is finalized. To do this, the thick layer 74 is removed so as to free the rear face of the sensitive layer 22. Then, the photodetectors 23 are produced for example by localized doping, for example by ion implantations or by localized diffusions in the rear face. Finally, at least one insulating passivation layer 24 is deposited on the sensitive layer 22 so as to cover it continuously.

[0069] With reference to [Fig.2F], the reflector 63 (advantageous) is then produced, followed by the interconnection stack 50. For this, a reflective layer 63 is deposited so as to continuously cover the insulating layer 24. This reflective layer 63 is made of a material suitable for reflecting the incident radiation to be detected, for example a metal such as Ti, Al, Cu and their alloys, or even heavily doped silicon. The thickness of the reflective layer is adapted according to the material used, and may be of the order of 400nm in the case of heavily doped silicon. The reflective layer 63 is then structured to form through openings intended for the passage of the conductive vias. Then, an insulating layer 64 is deposited so as to cover the reflective layer 63 and have a preferably flat rear face.

[0070] The conductive vias 32, 33, 34 are then produced, which are preferably made of the same materials. Thus, the conductive vias 32, 33, 34 extend here continuously, that is to say with continuity of the materials which constitute them, from the rear face of the lower insulating layer 64, to the photodiode 23 of the infrared detection pixel, to the electronic elements 42 of the reading stack 40, and to the electronic elements 14 of the visible detection pixels.

[0071] With reference to [Fig.2G], the interconnection stack 50 is then produced, starting with the upper metallization level 51, then the intermediate metallization levels 52, and finally the lower metallization level 53. In particular, certain conductive portions 51 of the upper metallization level are in contact with the conductive vias 32, 33, 34. Finally, a support substrate 31 is assembled to the interconnection stack 50. It should be noted that certain portions 51 of the upper metallization level (on the periphery of the detection matrices) may be in electrical contact with the external connection pads which will be produced at the very end of the process.

[0072] With reference to [Fig.2H], the structure obtained is then turned over, the handle layer 71 is removed so as to free one face of the upper insulating layer 11. The color filters 61 and the microlenses 62 are then produced. An imaging device 1 is thus obtained whose structural configuration has four stages: the visible matrix sensor 10, the reading stack 40 (assembled by molecular bonding to the visible matrix sensor 10), the infrared matrix sensor 20 (assembled by molecular bonding to the reading stack 40), and the interconnection stack 50. As indicated previously, this manufacturing method makes it possible to produce high-performance electronic elements of the reading stack 40, in particular by carrying out steps at high temperatures (around 1000°C), without this being able to degrade the photodiode 23 of the infrared detection pixels. External connection pads can also be produced.

[0073] [Fig. 3A] is a schematic and partial view, in cross-section, of an imaging device 1 according to an alternative embodiment. In this example, the imaging device 1 differs from that of [Fig. 1] essentially in that the sensitive layer 22 of the infrared matrix sensor 20 is not a continuous layer in the XY plane and common to all the detection pixels, but is formed of a plurality of sensitive layer portions, distinct from each other in the XY plane. The same sensitive layer portion 22 can extend opposite a single visible detection pixel, or, as here, opposite several adjacent pixels. In this example, a passivation layer 25, made of an electrically insulating material, covers the sides and the rear face of the sensitive layer 22. This passivation layer 25 is optional. The conductive vias 32, 33 (which connect the electronic elements Ironic 14 of the visible detection pixels and those 42 of the reading stack 40) therefore do not pass through the sensitive layer 22 of the infrared detection pixels.

[0074] [Fig. 3B] is a schematic and partial view, in cross-section, of an imaging device 1 according to an alternative embodiment similar to that of [Fig. 3A]. In this example, the imaging device 1 differs from that of [Fig. 3A] essentially in that the adjacent sensitive layer portions 22 are connected together two by two by connection portions 22r of lesser thickness, which correspond to non-completely etched portions of the initial sensitive layer 22 shown in [Fig. 2D]. These connection portions 22r are located on the side of the upper insulating layer 21. The conductive vias 32 and 34 pass through these connection portions 22r. This configuration is generally called “shallow MESA”.

[0075] [Fig. 4] is a schematic and partial view, in cross-section, of an imaging device 1 according to another alternative embodiment. In this example, the imaging device 1 differs from that of [Fig. 1] essentially in that electronic elements 14 of the visible detection pixels are not directly connected to the interconnection stack 50, each by the same conductive via. Indeed, the reading stack 40 comprises at least one electrical routing level formed of conductive portions 45.

[0076] More precisely, conductive portions 45 are located within the lower insulating layer 16 and extend in a planar manner. Certain areas of these conductive portions 45 are in electrical contact with the electronic elements 14 of the visible detection pixels, other areas are in electrical contact with the conductive vias 32. There is therefore an indirect electrical connection between the electronic elements 14 and the interconnection stack 50, via the conductive portions 45. Here, a single routing level (formed by the conductive portions 45) is shown, but several routing levels are obviously possible. These conductive portions 45 can be produced before the bonding step illustrated in [Fig.2B], for example based on doped silicon.

[0077] [Fig. 5] is a schematic and partial view, in cross-section, of an imaging device 1 according to another alternative embodiment. In this example, the imaging device 1 differs from that of [Fig. 1] essentially in that it comprises an additional reading substrate 80, assembled to the interconnection stack 50 on the rear face and electrically connected to the latter. Thus, the reading substrate 80 comprises an interconnection stack 82, assembled by molecular bonding, for example a hybrid copper / oxide molecular bonding to the interconnection stack 50, and a reading stack 81. Thus, the imaging device 1 here comprises two integrated reading circuits, one 40, 50 of which the reading stack 40 is located between the visible matrix sensor 10 and the infrared matrix sensor 20 and of which the interconnection stack 50 is located on the rear face of the infrared matrix sensor 20, and the other 80 which is assembled to the interconnection stack 50. This allows the imaging device 1 to distribute the electronic control functions of the visible 10 and infrared 20 matrix sensors on the two integrated reading circuits 40, 50, 80.

[0078] Particular embodiments have just been described. Different variants and modifications will appear to those skilled in the art.

Claims

Claims

1. Imaging device (1), adapted to acquire a visible image and an infrared image, comprising: • a visible matrix sensor (10), comprising a first sensitive layer (12) in which visible detection pixels are defined comprising at least one electronic element (14); • an infrared matrix sensor (20), comprising a second sensitive layer (22), superimposed on the first sensitive layer (12), in which infrared detection pixels are defined comprising at least one electronic element (23); • an integrated reading circuit (40, 50), superimposed on the visible matrix sensor (10) and on the infrared matrix sensor (20), formed of a reading stack (40) comprising electronic elements (42) and an interconnection stack (50);• characterized in that the reading stack (40) is located between the first sensitive layer (12) and the second sensitive layer (22), and in that the interconnection stack (50) is located on the rear face of the infrared matrix sensor (20), • conductive vias (32, 33, 34) electrically connect, respectively, the interconnection stack (50) to the electronic elements (14) of the visible matrix sensor (10), to the electronic elements (42) of the reading stack (40), and to the electronic elements (23) of the infrared matrix sensor (20).;

2. Imaging device (1) according to claim 1, wherein the visible matrix sensor (10) comprises a first insulating layer (16) located under the first sensitive layer (12), and wherein the reading stack (40) comprises a second insulating layer (41) located above the electronic elements (42) of the reading stack (40), the first insulating layer (16) and the second insulating layer (41) being in contact with each other.

3. Imaging device (1) according to claim 1 or 2, wherein the reading stack (40) comprises a third insulating layer (43) located under the electronic elements (42) of the reading stack (40), and wherein the infrared matrix sensor (20) comprises a fourth insulating layer (21) located above the second sensitive layer (22), the third insulating layer (43) and the fourth insulating layer (21) being in contact with each other.

4. An imaging device (1) according to any one of claims 1 to 3, wherein conductive vias (34) extend directly from the electronic elements (23) of the infrared matrix sensor (20) to conductive portions (51) of the interconnect stack (50).

5. An imaging device (1) according to any one of claims 1 to 4, wherein conductive vias (33) extend directly from the electronic elements (42) of the read stack (40) to conductive portions (51) of the interconnect stack (50).

6. An imaging device (1) according to any one of claims 1 to 5, wherein conductive vias (32) extend directly from the electronic elements (14) of the visible matrix sensor (10) to conductive portions (51) of the interconnect stack (50).

7. Imaging device (1) according to any one of claims 1 to 5, wherein conductive vias (32) extend directly from conductive portions (45) of the read stack (40), which are in electrical contact with the electronic elements (14) of the visible matrix sensor (10), to conductive portions (51) of the interconnect stack (50).

8. Imaging device (1) according to any one of claims 1 to 7, wherein the second sensitive layer (22) is a layer structured in a plane parallel to the plane of the infrared matrix sensor (20) forming a plurality of portions of second sensitive layer (22), distinct from each other in the parallel plane, so that the conductive vias (32, 33) electrically connecting, respectively, the interconnection stack (50) on the one hand to the electronic elements (14) of the visible matrix sensor (10) and to the electronic elements (42) of the reading stack (40) on the other hand, do not pass through the second sensitive layer (22).

9. Imaging device (1) according to any one of claims 1 to 7, wherein the second sensitive layer (22) is a layer structured in a plane parallel to the plane of the infrared matrix sensor (20) forming a plurality of portions of second sensitive layer (22) connected two by two by a connection portion (22r) of lesser thickness, so that the conductive vias (32, 33) electrically connecting, respectively, the interconnection stack (50) on the one hand to the electronic elements (14) of the visible matrix sensor (10) and to the electronic elements (42) of the reading stack (40) on the other hand, pass through the connection portions (22r).

10. An imaging device (1) according to any one of claims 1 to 9, wherein the read stack (40) and the interconnect stack (50) are first read stacks (40) and interconnect stacks of a first read integrated circuit (40, 80), and wherein a second read integrated circuit (80), formed of second read stacks (81) and interconnect stacks (82), is assembled to the first read integrated circuit (40, 50), the second interconnect stack (82) being assembled and connected to the back face of the first interconnect stack (50).

11. Imaging device (1) according to any one of claims 1 to 10, comprising a reflective layer (63), located between the infrared matrix sensor (20) and the interconnection stack (50), adapted to reflect incident infrared radiation intended to be detected by the infrared matrix sensor (20).

12. Imaging device (1) according to claim 11, wherein the reflective layer (63) forms, with the infrared matrix sensor (20), the reading stack (40) and an insulating layer (16) located between the first sensitive layer (12) and the reading stack (40), an optical cavity resonant at the wavelength of the infrared radiation.

13. Method for manufacturing an imaging device (1) according to any one of the preceding claims, comprising the following steps: • production of the visible matrix sensor (10), a first insulating layer (16) covering the first sensitive layer (12) where the electronic elements (14) are flush; • production of a first structure intended to form the reading stack (40), comprising a second insulating layer (41), by molecular bonding of the second insulating layer (41) on the first insulating layer (16), then production of the reading stack (40); • production of a second structure intended to form the infrared matrix sensor (20), comprising a fourth insulating layer (21), by molecular bonding of the fourth insulating layer (21) on a third insulating layer (43) of the reading stack (40), then production of the infrared matrix sensor (20); • production of the interconnection stack (50) from the rear face of the infrared matrix sensor (20).

14. Manufacturing method according to claim 13, wherein, during the step of producing the electronic elements (42) of the reading stack (40), a temperature increase to a temperature at least equal to 1000°C is carried out.

15. Manufacturing method according to claim 13 or 14, wherein the step of producing the electronic elements (23) of the infrared matrix sensor (20) is carried out after the step of producing the electronic elements (42) of the reading stack (40).

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