Electromagnetic radiation detection device comprising a thermal detector on a reading substrate, an active electronic element of which is located as close as possible to the thermal detector

Abstract

The invention relates to a device for detecting electromagnetic radiation, comprising at least one sensitive pixel including a thermal detector (10), and comprising a readout substrate (20) formed by a stack of a readout structure (23) and an interconnection structure (22). The thermal detector includes a suspended absorbing membrane (11) and anchoring pillars (13). The readout structure (23) is located on and in contact with the interconnection structure (22); the first active electronic element (23.1a) is connected directly to the upper metallization layer; and the anchoring pillars (13) extend continuously into the readout substrate (20) until they come into contact with the upper metallization layer. Figure for the abstract: Fig. 1A

Description

Title of the invention: Device for detecting electromagnetic radiation comprising a thermal detector on a reading substrate of which an active electronic element is located as close as possible to the thermal detector Technical field

[0001] The field of the invention is that of devices for detecting electromagnetic radiation, comprising at least one thermal detector with an absorbent membrane suspended above a reading substrate and thermally insulated therefrom. The invention applies in particular to the field of infrared or terahertz imaging, thermography, or even gas detection. STATE OF THE PRIOR ART

[0002] An electromagnetic radiation detection device may comprise sensitive pixels each formed of a thermal detector comprising an absorbent membrane suspended and thermally insulated from a reading substrate. The absorbent membrane comprises an absorber of the electromagnetic radiation to be detected, associated with a thermometric transducer whose electrical property varies in intensity as a function of the heating of the transducer. Such a thermometric transducer may be a thermistor (for example, a vanadium or titanium oxide, or even amorphous silicon), a diode (pn or pin junction), or even a metal oxide semiconductor field effect transistor (MOSFET).

[0003] Since the temperature of the thermometric transducer is dependent on its environment, the absorbing membrane is thermally insulated from the reading substrate. For this purpose, the absorbing membrane is generally suspended above the reading substrate by anchoring pillars, and is thermally insulated from it by thermal insulation arms. These anchoring pillars and thermal insulation arms also have an electrical function by ensuring the electrical connection of the absorbing membrane to the reading circuit.

[0004] According to a configuration called 'above IC' (i.e. above the integrated circuit), described in particular in document EP2743659A1, the thermal detectors are produced above the reading circuit located in the support substrate. The reading circuit is in the form of a CMOS integrated circuit, and comprises an interconnection structure located above a reading structure.

[0005] The interconnection structure, or BEOL structure (for Back End Of Line, in English), is formed of surface layers where levels of metallization, which are separated vertically by intermetal dielectric (IMD) layers, and are connected to each other by conductive vias.

[0006] The reading structure, or FEOL structure (for Front End Of Line, in English), is formed of deep layers based on semiconductor where active electronic elements (diodes, transistors, etc.) and possibly passive electronic elements (capacitors, resistors, etc.) are made. The electronic elements are connected by the metallization levels to the thermal detectors on the one hand, and to at least one external connection pad on the other hand, the latter being intended to connect the detection device to an external electronic device.

[0007] As described in particular in document EP2894445A1, each sensitive pixel may comprise an active electronic element such as an injection MOS transistor, connected to the corresponding thermal detector, by the metallization levels of the interconnection structure. The reading circuit of each sensitive pixel may be connected to that of one or more compensation thermal detectors located for example at the bottom of the column of the detection matrix, and to a capacitive transimpedance amplifier (CTIA).

[0008] There is, however, a need to improve the performance of such a detection device. Statement of the invention

[0009] The invention aims to remedy at least in part the drawbacks of the prior art, and more particularly to propose a detection device which has improved electrical performance, in particular in terms of impulse response (limitation of the parasitic capacitance at the reading node of the sensitive element of the pixel), or even in terms of access resistance. The detection device comprises at least one thermal detector with a membrane suspended above a reading substrate. The original structural configuration of the reading substrate not only makes it possible to improve these electrical performances of the detection device, but also leads to better mechanical maintenance of the anchoring pillars.

[0010] For this, the subject of the invention is a device for detecting electromagnetic radiation, comprising at least one sensitive pixel comprising a thermal detector, and comprising a reading substrate, comprising a reading circuit, which is formed from a stack of: a reading structure containing active electronic elements of the reading circuit, including at least a first active electronic element located in the sensitive pixel and connected to the thermal detector; and an interconnection structure containing different levels of metallization connected to active electronic elements, including a higher metallization level located on the side of an upper face of the reading substrate.

[0011] The thermal detector comprises: an absorbent membrane, suspended above an upper face of the reading substrate and thermally insulated from the latter; and anchoring pillars, ensuring the suspension of the absorbent membrane and the electrical connection of the latter to the reading circuit.

[0012] According to the invention, the reading structure is located on and in contact with the interconnection structure; the first active electronic element is connected directly to the upper metallization level; and the anchoring pillars extend continuously in the reading substrate until they come into contact with the upper metallization level.

[0013] Some preferred but non-limiting aspects of this detection device are as follows.

[0014] The upper metallization level may comprise several coplanar conductive portions, including a first conductive portion to which a first anchoring pillar of the sensitive pixel comes into contact, and to which the first active electronic element is connected by means of a first conductive via.

[0015] The active electronic elements can be connected directly to coplanar conductive portions of the upper metallization level by conductive vias, said conductive vias and the anchoring pillars being made of the same materials.

[0016] The reading substrate may comprise an upper structure located on and in contact with the reading structure. The reading structure may comprise: a first insulating layer in which the active electronic elements are located and through which conductive vias extend between the active electronic elements and conductive portions of the upper metallization level; and a second insulating layer which extends on and in contact with the insulating layer and the active electronic elements. In addition, the upper structure may comprise: a third insulating layer, which extends on and in contact with the second insulating layer; and a reflector resting on the third insulating layer.

[0017] The upper structure may comprise a thin protective layer, made of a material inert to hydrofluoric acid, extending above the third insulating layer, the first, second and third insulating layers being made of a mineral material.

[0018] The reflector may be a Bragg mirror formed of several thin layers spaced vertically from each other and held by conductive vias passing through said thin layers.

[0019] The reading substrate may be a first reading substrate to which a second reading substrate is assembled and electrically connected at a face opposite the upper face of the first reading substrate, the second substrate reading comprising a stack of a second reading structure and a second interconnection structure, in which: conductive portions of a lower metallization level of the second interconnection structure are connected to active electronic elements of the second reading structure; and conductive portions of a higher metallization level of the second interconnection structure are in contact with conductive portions of a lower metallization level of the interconnection structure of the first reading substrate.

[0020] The detection device may comprise an external connection pad intended to be electrically connected to an external electronic system, extending through the reading structure to come into contact with at least one conductive portion of the upper metallization level.

[0021] The invention also relates to a method of manufacturing a detection device according to any one of the preceding characteristics, comprising the following steps: - production of a first stack comprising a handle on which rests a sacrificial layer made of a mineral material; - transfer and molecular bonding, on the first stack, of an SOI substrate formed from a silicon substrate, an oxide layer then a thin layer of silicon, then removal of the silicon substrate; - production of the reading structure, the active electronic elements being produced from the thin layer of silicon on SOI substrate; - production of the interconnection structure on the reading structure, conductive portions of the upper metallization level being directly connected to the active electronic elements by conductive vias; - turning over the resulting stack, then removing the handle; - production of the absorbent membrane on the sacrificial layer; - removal of the sacrificial layer so as to suspend the absorbent membrane.

[0022] The production of the reading structure may include the following steps: - deposition of a first insulating layer covering the active electronic elements; - production of conductive vias, extending through the first insulating layer to come into contact with the active electronic elements; - production of anchor pillars, extending through the first insulating layer and the sacrificial layer to come into contact with the handle.

[0023] The method may comprise, before the molecular transfer and bonding step, a step of producing an upper structure, resting on the sacrificial layer, comprising a reflector and a thin protective layer, which are covered by a third insulating layer.

[0024] The thin silicon layer of the SOI substrate can be covered with a second insulating layer, so that, during transfer and molecular bonding, the second insulating layer is brought into contact with the third insulating layer.

[0025] During the step of producing the absorbent membrane, a thermometric transducer, for example a thermistor, can be produced.

[0026] Alternatively, during the step of producing the first stack, a thermometric transducer, for example a junction diode or a transistor, can be produced on the handle, then be covered by the sacrificial layer. Brief description of the drawings

[0027] 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:

[0028] [Fig.1A] is a schematic and partial view, in cross-section, of a detection device according to an embodiment where the reading substrate comprises a reading structure located on the interconnection structure;

[0029] [Fig.1B] is a schematic and partial view, in cross-section, of a detection device according to an alternative embodiment;

[0030] Figures 2A to 2H illustrate different steps of a method of manufacturing a detection device identical or similar to that of [Fig.1A];

[0031] Figures 3A to 31 illustrate different steps of a method of manufacturing a detection device identical or similar to that of [Fig.lB];

[0032] Figures 4A and 4B illustrate different steps of a method of manufacturing a detection device similar to that of [Fig.lB], where the reflector is a Bragg mirror;

[0033] Figures 5A to 5D illustrate different steps of a method of manufacturing a detection device similar to that of [Fig.lB], where a second reading substrate is assembled and connected on the rear face to the first reading substrate.

[0034] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0035] In the figures and in the remainder of the description, the same references represent identical or similar elements. In addition, the different elements are not shown to scale so as to enhance the clarity of the figures. Furthermore, the different embodiments and variants are not mutually exclusive and may 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%. elsewhere, the terms "between ... and ..." and equivalents mean that the limits are included, unless otherwise stated.

[0036] The invention relates to a device for detecting electromagnetic radiation, for example infrared or terahertz radiation. The detection device can thus be particularly suitable for detecting infrared radiation in the LWIR (Long Wavelength Infrared) range, the wavelength of which is between approximately 8 pm and 14 pm.

[0037] The detection device comprises at least one sensitive pixel, and preferably a matrix of sensitive pixels. A sensitive pixel is formed of a thermal detector, intended to absorb electromagnetic radiation, and electrically connected to a reading circuit located in the substrate on which it rests.

[0038] The thermal detector is of the absorbent membrane type, which is suspended above the reading substrate by thermal insulation arms 12 and anchoring pillars. The pillars and arms provide the electrical connection of the absorbent membrane to the reading circuit. The absorbent membrane comprises a thermometric detection transducer, i.e. an element having an electrical property varying with its heating. Such a transducer may be a thermistor based on vanadium or titanium oxide, or even amorphous silicon. It may also be a pn or pin junction diode, or be a MOS field effect transistor (MOSFET).

[0039] The reading substrate is formed from a stack of an interconnection structure (BEOL type) and a reading structure (FEOL type). Each sensitive pixel comprises at least one active electronic element of the reading structure (e.g. a MOS transistor), connected to the thermal detector by the upper metallization level of the interconnection structure. Furthermore, the interconnection structure ensures the electrical connection of the sensitive pixels to other active electronic elements of the reading circuit, as well as to an external connection pad.

[0040] The interconnection levels are each formed of coplanar conductive portions, these being connected to those of the adjacent interconnection levels by conductive vias. The interconnection structure therefore comprises several parallel interconnection levels arranged vertically to each other. It thus comprises a first interconnection level, called upper, and located on the side of the thermal detector, intermediate interconnection levels, and a last interconnection level, called lower, and located on the side opposite the thermal detector.

[0041] According to the invention, in the reading substrate, the reading structure is located on the interconnection structure, i.e. above it. In other words, it is located on the side of the thermal detector while the interconnection structure is located on the opposite side. This configuration is the reverse of the usual configuration in the prior art detection devices, where the FEOL type reading structure is located under the BEOL type interconnection structure.

[0042] Furthermore, a first active electronic element of the sensitive pixel (for example the MOS transistor) is connected directly to the upper metallization level, i.e. without passing through intermediate metallization levels. This configuration is also the reverse of what is usually done in the prior art where the injection MOS transistor is generally connected to the lower metallization level.

[0043] Finally, the anchoring pillars extend continuously in the reading substrate until they come into contact with the upper metallization level. By extending continuously, it is meant that the anchoring pillars extend without discontinuity of the materials which constitute them up to the upper metallization level. The anchoring pillars therefore have a lower part which is located inside the reading substrate, which makes it possible to improve their mechanical strength.

[0044] Also, in the same sensitive pixel, the anchoring pillars and the first active electronic element are in contact with the upper metallization line. This structural configuration makes it possible to improve the electrical performance of the detection device, insofar as the access resistance and the parasitic capacitances are reduced, while reinforcing the mechanical strength of the anchoring pillars.

[0045] [Fig.1A] is a schematic and partial cross-sectional view of a detection device 1 according to one embodiment. In this example, the transducer 11.1 is a thermistor.

[0046] Here and for the remainder of the description, a direct three-dimensional orthogonal reference frame XYZ is defined, where the XY plane is substantially parallel to the main plane of the reading substrate 20, and where the Z axis is oriented in the direction of the absorbent membrane 11. In the remainder of the description, the terms “lower” and “upper” are understood as relating to an increasing positioning when moving away from the reading substrate 20 in the +Z direction.

[0047] The reading substrate 20 here comprises a stack formed of a support substrate 21, an interconnection structure 22 (BEOL), a reading structure 23 (FEOL), and finally here an upper structure 24 which comprises a reflector 24.3.

[0048] The support substrate 21 is an optional substrate on which the interconnection structure 22 rests and is in contact. It is a handle which was used during the manufacturing process (see [Fig.2A] to 2H). Here it is a silicon substrate thick, for example several hundred microns.

[0049] The interconnection structure 22 is a part of the reading substrate 20 which comprises a plurality of metallization levels parallel to each other. Each metallization level comprises coplanar conductive portions, connected to the conductive portions of the adjacent metallization levels by conductive vias 22.4. The conductive vias 22.4 pass through insulating layers 22.5 called inter-metal dielectric (IMD), which separate the metallization levels two by two. The interconnection structure 22 ensures the electrical connection, for each sensitive pixel, between the absorbent membrane 11 and the active electronic element(s) 23.1 associated with the absorbent membrane 11 in question. It also ensures the electrical connection of each sensitive pixel to any other reading system adapted to reading the electrical information delivered by the detection device, or even to other active electronic elements, for example to a capacitive transimpedance amplifier (CTIA) located at the bottom of the column (in the case where the transducer is a thermistor), this CTIA also being connected to one or more thermal compensation detectors. Finally, it ensures the electrical connection to an external connection pad 2 (see [Fig.2H]).

[0050] The metallization levels therefore comprise, along the -Z direction, a first metallization level, or upper metallization level, formed of the conductive portions 22.1, and located on the side of the upper face of the reading substrate 20, and a last metallization level, or lower metallization level, formed of the conductive portions 22.3, and located on the side of the lower face of the reading substrate 20. Intermediate metallization levels (conductive portions 22.2) are present between the upper and lower levels. It is then understood that there are no metallization levels of the interconnection structure 22 located above the upper level, that is to say located between the upper face and the upper metallization level. The conductive portions 22.1, 22.2 and 22.3 and the conductive vias 22.4 may be made, for example, from copper, aluminum or tungsten, among others. The insulating layers 22.5 are made of a mineral material, for example, based on silicon oxide or nitride.

[0051] The reading structure 23 is a part of the reading substrate 20 which comprises the active or passive electronic elements which are connected to the sensitive pixels, or even to one or more compensation pixels. The active electronic elements 23.1 may be of the transistor or diode type (for example photodiode, light-emitting diode, etc.), and the passive electronic elements may be capacitors, resistors, etc. The reading structure 23 is located above the interconnection structure 22 along the vertical axis Z, that is to say it is located between the upper face of the reading substrate 20 and the interconnection structure 22.

[0052] For each sensitive pixel, the active electronic elements 23.1 are connected to the upper metallization level, and more precisely to the conductive portions 22.1 by means of conductive vias 23.2. The active electronic elements 23.1 are located here under the absorbent membrane 11 in the XY plane, and above the upper metallization level. The active electronic elements 23.1 are here directly connected to the conductive portions 22.1 by the conductive vias 23.2, that is to say that each conductive via 23.2 is in contact with an active electronic element 23.1 and a conductive portion 22.1. One or more vias 23.2 may also be connected to one or more passive electronic elements. Unless otherwise indicated, when referring to two elements connected directly to each other, it is understood that they are connected by a conductive via, without passing through an intermediate metallization level.

[0053] Other active electronic elements 23.1 are located at the bottom of the column, in particular to define the CTIA mentioned above. They are therefore offset in the XY plane relative to the sensitive pixels. They are also located between the upper face and the interconnection structure 22.

[0054] According to one embodiment, in each sensitive pixel, a first active electronic element 23.1a is directly connected to a first conductive portion 22.1a of the upper metallization level by at least one first conductive via 23.2a. As described later, this conductive portion 22.1a is also in contact with one of the anchoring pillars 13. This configuration makes it possible to reduce the access resistance between the active electronic element 23.1a, for example here the injection MOS transistor, and the absorbing membrane 11, and also to reduce the parasitic capacitances.

[0055] The conductive vias 23.2 of the active electronic elements 23.1, directly connecting the latter to the upper metallization level, may be made of the same material(s) as those of the anchoring pillars 13. For example, the conductive vias 23.2 may be formed of an envelope, for example of Ti / TiN or Ta / TaN, as described in particular in the document EP2743659 mentioned above) which surrounds a core of copper Cu and / or tungsten W. The active electronic elements 23.1 are made from a semiconductor layer 43 (see [Fig.2C] to 2E), made for example from silicon, and are surrounded by one or more insulating layers 23.3 and 23.4 made of a dielectric material. In this example, the active electronic elements 23.1 are located in an insulating layer 23.3 and are covered with an insulating layer 23.4. This insulating layer 23.4 is made of an oxide, and is bonded by oxide / oxide molecular bonding with an insulating layer 24.1 also made of an oxide. This step of transfer and molecular bonding is described further with reference to [Fig.2D].

[0056] The upper structure 24 here comprises the insulating layer 24.1, a thin protective layer 24.2 and a reflector 24.3. The thin protective layer 24.2 here extends over and in contact with the insulating layer 24.1. It is adapted to ensure protection of the reading substrate 20 against a chemical attack, for example in an HF acid medium (hydrofluoric acid), implemented to etch the mineral layer(s) sacrificial layers used during the production of the detection device 1. This thin protective layer 24.2 thus forms a hermetic and chemically inert layer ensuring protection of the underlying inter-metal dielectric layers 22.5 against chemical attack, and is electrically insulating to prevent any short circuit. It can be made of alumina A12O3, or even of aluminum nitride or fluoride, and can have a thickness of between a few tens and a few hundreds of nanometers, for example between 100 nm and 500 nm.

[0057] The reflector 24.3 is adapted to reflect the light radiation to be detected in the direction of the absorbing membrane 11. It is located under the latter in the XY plane, and forms with it a quarter-wave interference optical cavity, making it possible to maximize the absorption of the light radiation by the absorbing membrane 11. In this example, the reflector 24.3 is on and in contact with the thin protective layer 24.3, but it is possible to make it in contact with the insulating layer 24.1 and to cover it with the thin protective layer 24.2. It can be made of at least one layer of silicon a few hundred nanometers thick, heavily doped with a doping level at least equal to 1019 cm 3.

[0058] The thermal detector 10 comprises an absorbent membrane 11, suspended above the reading substrate 20 by thermal insulation arms 12 and anchoring pillars 13. The absorbent membrane 11 comprises the thermometric transducer 11.1, here a thermistor. The thermal insulation arms 12 and the anchoring pillars 13 are electrically conductive, and ensure the electrical connection of the thermistor 11.1 to the reading circuit. The absorbent membrane 11 and the thermal insulation arms 12 are elements known to those skilled in the art. In this example, the arms 12 and here the absorbent membrane 11 are formed from a stack of a lower insulating layer 12.1, a conductive layer 12.2, and an upper insulating layer 12.3. The conductive layer 12.2 extends horizontally, in the XY plane, until it comes into contact with the thermistor 11.1 to ensure the electrical polarization of the latter.Furthermore, the absorbing membrane 11 comprises an absorbing layer 11.2 (for absorbing the light radiation to be detected), located above the thermistor 11.1 and resting on an intermediate insulating layer. The absorbing layer 11.2 is covered by the upper insulating layer 12.3. It can be made of TiN with a thickness of approximately 8nm to 15nm so as to obtain a sheet resistance of approximately 377Q / square.

[0059] The anchoring pillars 13 can be made from a casing, for example, made of Ti / TiN or Ta / TaN, and a core, for example, made of Cu and / or W. They extend vertically, along the Z axis, up to the thermal insulation arms 12, and each come into contact with a conductive portion 22.1 of the upper metallization level. Also, they pass through the thin protective layer 24.2, the insulating layer 24.1, as well as the insulating layers 23.4 and 23.3 of the reading structure 23. Thus, they extend continuously along the Z axis to come into contact with the conductive portions 22.1 of the upper metallization level. By extend continuously, it is meant here that there is a continuity of material of the anchoring pillars 13 between the arms 13 and the conductive portions 22.1. In particular, they do not come into contact with conductive portions which would be located above the upper metallization level. Thus, each anchoring pillar 13 has a lower part which is surrounded by the dielectric material of the insulating layers of the reading substrate 20 (here 24.2, 24.1, 23.4 and 23.3). In addition, at least one of the anchoring pillars 13 comes into contact with the first conductive portion 22.1a of the upper metallization level to which the first active electronic element 23.1a is directly connected.

[0060] Thus, by the arrangement of the reading structure 23 on the interconnection structure 22, and by the fact that the anchoring pillars 13 extend continuously until they come into contact with the conductive portions 22.1 of the upper metallization level, it is possible to connect, for each sensitive pixel, at least one active electronic element 23.1 directly to the conductive portions 22.1 of the upper metallization level, and in particular to one of them (22.1a) with which one of the anchoring pillars 13 is in contact. Thus, both the mechanical strength of the anchoring pillars 13 is improved, but also the access resistance and the parasitic capacitances are reduced. The electrical performance of the detection device 1 is improved, for example in terms of impulse response and reading speed.Furthermore, as detailed below, this configuration makes it possible to simply implement manufacturing processes for the detection device 1, which differ from each other in particular by the fact that the transducer 11.1 supports, or does not support, the high temperatures (around 1000°C) of the production of the active electronic elements 23.1. In the example of [Fig.lA], the transducer 11.1 is a thermistor which does not support these high temperatures.

[0061] [Fig.lB] is a schematic and partial cross-sectional view of a detection device 1 according to one embodiment. In this example, the transducer 11.1 is a diode (which withstands the high temperatures, of the order of 1000°C, necessary for the production of the active electronic elements 23.1). The diode 11.1 is formed from a semiconductor layer and has p-type and n-type doped portions, so as to form, at the level of the absorbing membrane 11, a pn semiconductor junction. The diode 11.1 is here made from silicon, preferably monocrystalline. The absorbing membrane 11 comprises a lower insulating layer 11.3 (passivation), on which the diode 11.1 rests and is in contact. On the diode 11.1 rests a stack of an insulating layer 12.1, a conductive layer 12.2, and an upper insulating layer 12.3. At the membrane level absorbing layer 11, the conductive layer 12.2 comes into contact with the p- and n-type doped portions of the diode 11.1, and ensures their electrical polarization. Here, it extends above the diode 11 and forms an absorbing layer for the light radiation to be detected.

[0062] Figures 2A to 2H illustrate different steps of a method for manufacturing a detection device 1 identical or similar to that of [Fig.lA]. In this example, the reflector 24.3 is made of a material which withstands the high temperatures of the production of the active electronic elements 23.1, and is therefore here produced before the latter. On the other hand, the thermistor 11.1 does not withstand these high temperatures, and is therefore produced after the active electronic elements 23.1.

[0063] With reference to [Fig.2A], a sacrificial layer 32, made of a mineral material such as a silicon oxide or nitride, is deposited on a handle 31. The sacrificial layer 32 is intended to allow the subsequent production of the absorbent membrane 11. Its thickness will define the distance of the quarter-wave optical cavity between the absorbent membrane 11 and the reflector 24.3.

[0064] With reference to [Fig.2B], the reflector 24.3 is then produced, followed by the thin protective layer 24.2. For this, a continuous layer 33 of overdoped silicon is deposited on and in contact with the sacrificial layer 32. Then, the reflector 24.3 is produced by lithography and localized etching of the silicon layer 33. Openings 34 are formed in the silicon layer 33 so as to subsequently allow the anchoring pillars 13 to be produced. Then, the thin protective layer 24.2 is deposited in a conformal manner, so as to continuously cover the reflector 24.3 and to descend into the openings 34 to come into contact with the sacrificial layer 32. Finally, the insulating layer 24.1, made of an oxide, is deposited so as to cover the thin protective layer. Planarization is then carried out. This stack of the reflector 24.3, the thin protective layer 24.2 and the insulating layer 24.1 forms the upper structure 24 of the reading substrate 20. .

[0065] With reference to [Fig.2C], a bonding of an SOI substrate 40 (silicon substrate 41, buried oxide layer 42, then thin layer of silicon 43, preferably monocrystalline) is ensured on the insulating layer 24.1. The bonding here is an oxide / oxide molecular bonding. For this, an insulating layer 23.4, made of an oxide, is deposited beforehand on the thin layer of silicon 43. The insulating layers 23.4 and 24.1 are then brought into contact to ensure molecular bonding.

[0066] With reference to [Fig.2D], the silicon substrate 41 is removed (the buried oxide layer 42 can be kept at least in part), then the active electronic elements 23.1 and 23.1a are produced (lithography, etching, deposition, doping, etc.). During these steps, a high temperature can be applied, of the order of 1000°C. However, the reflector 24.3 is made here of a material that can withstand these high temperatures. An insulating layer 23.3 made of a dielectric material is then deposited, here in an oxide, so as to cover the active electronic elements 23.1, 23.1a. Then, the anchoring pillars 13 are produced as well as the conductive vias 23.2. They are then preferably made of the same materials. The anchoring pillars 13 extend here continuously, i.e. with continuity of the materials which constitute them, from the upper face of the insulating layer 23.3 to the handle 31. They therefore pass through the insulating layer 23.3, the insulating layer 23.4, the insulating layer 24.1, the thin protective layer 24.2, and finally the sacrificial layer 32. The conductive vias 23.2 pass through the insulating layer 23.3 and come into contact with the active electronic elements 23.1, 23.1a. Planarization is then carried out.

[0067] With reference to [Fig.2E], the interconnection structure 22 is then produced, starting with what will be the upper metallization level, then the intermediate metallization levels, and finally the lower metallization level. In particular, the conductive portions 22.1 of the upper metallization level are in contact with the conductive vias 23.2 of the active electronic elements 23.1. The latter are thus directly connected to the upper metallization level. In addition, the same conductive portion 22.1a of the upper metallization level is in contact with an anchoring pillar 13 and a conductive via 23.2a which ensures the connection with the active electronic element 23.1a, here an injection MOS transistor. Finally, a support substrate 21 is assembled to the interconnection structure 22.

[0068] With reference to [Fig.2F], the stack produced is turned over, and the handle 31 is removed, so as to free one face of the sacrificial layer 32. Then, the thermal insulation arms 12 and the absorbent membrane 11 are produced on the sacrificial layer 32. The thermal insulation arms 12 are in contact with one end of the anchoring pillars 13 which have been produced beforehand.

[0069] With reference to [Fig.2G], the external connection pad 2 is produced through the sacrificial layer 32, so as to come into contact with at least one conductive portion 22.1 of the upper metallization level. The external connection pad 2 is produced from at least one metal layer, deposited in a notch formed through the sacrificial layer 32, the thin protective layer 24.2, and the underlying insulating layers.

[0070] With reference to [Fig.2H], the absorbent membrane 11 is released by removing the sacrificial layer 32, here by chemical etching by HF in the vapor phase. The external connection pad 2 may comprise a peripheral upper part 2b which extends laterally preferably over at least 5 μm from the vertical part 2a. Thus, during the HF vapor etching, an unetched portion of the sacrificial layer 32 may be located under the peripheral upper part 2b, which makes it possible to reinforce the mechanical strength of the external connection pad 2.

[0071] Thus, the manufacturing method makes it possible to produce a detection device 1 whose electrical performance, as well as the mechanical strength of the anchoring pillars 13, are improved. In this method, the thermistor 11.1 is sensitive to the high temperatures generated during the production of the active electronic elements 23.1, which explains why it is produced after the latter.

[0072] Figures 3A to 31 illustrate different steps of a method for manufacturing a detection device 1 identical or similar to that of [Fig.lB]. This method differs from that of [Fig.2A] to 2H essentially in that the thermometric transducer 11.1 is a pn junction diode produced before the reading structure 23. Several steps are identical or similar to those of the method of [Fig.2A] to 2H and are therefore only briefly described.

[0073] With reference to [Fig.3A], an SOI substrate 50 is provided, formed of a silicon substrate 51, a buried oxide layer 52, then a thin layer of silicon 53, preferably monocrystalline.

[0074] With reference to [Fig.3B], the thermometric transducer 11.1, here a pn junction diode, is produced from the thin silicon layer 53. For this, the thin silicon layer 53 is structured by lithography and localized etching, and the p-type and n-type doped portions are produced by localized ion implantation. Lateral semiconductor pads 13.1, originating from the thin silicon layer 53 and preferably doped, can be produced and are intended to be located at the top of the anchoring pillars 13. Furthermore, a thin passivation layer 11.3 can be deposited so as to cover only the transducer 11.1.

[0075] With reference to [Fig.3C], a sacrificial layer 32 made of a mineral material, for example silicon oxide, is deposited so as to cover the transducer 11.1, the lateral semiconductor pads 13.1, and the buried oxide layer 52. This sacrificial layer 32 has a thickness which will define the dimension of the quarter-wave optical cavity between the absorbent membrane 11 and the reflector 24.3. The reflector 24.3 is then produced, then the thin protective layer 24.2, and finally the insulating layer 24.1, in a manner identical or similar to that described with reference to [Fig.2B].

[0076] With reference to [Fig.3D], an SOI substrate 40 (silicon substrate 41, buried oxide layer 42, thin silicon layer 43, preferably monocrystalline), covered by the insulating layer 23.4 made of an oxide, is transferred and bonded to the insulating layer 24.1. The bonding here is an oxide / oxide molecular bonding.

[0077] With reference to [Fig.3E], the substrate 4L is removed. Then the reading structure 23 and its active electronic elements 23.1, 23.1a are produced. During these steps, the stack can be subjected to high temperatures, of the order of 1000°C, which however does not alter the properties of the transducer 11.1 or those of the reflector 24.3.

[0078] Finally, the anchoring pillars 13 and the conductive vias 23.2 are produced. The anchoring pillars 13 extend continuously from the upper face of the insulating layer 23.3 to the silicon substrate 51. They therefore pass through the insulating layer 23.3, the insulating layer 23.4, the insulating layer 24.1, the thin protective layer 24.2, and finally the sacrificial layer 32, to come into contact with the lateral semiconductor pads 13.1. The conductive vias 23.2 pass through the insulating layer 23.3 and come into contact with the active electronic elements 23.1, 23.1a. Planarization is then carried out.

[0079] With reference to [Fig.3F], the interconnection structure 22 is produced, starting with what will be the upper metallization level, then the intermediate metallization levels, and finally the lower metallization level. The conductive portions 22.1 of the upper metallization level are in contact with the conductive vias 23.2 of the active electronic elements 23.1. In addition, the same conductive portion 22.1a of the upper metallization level is in contact with an anchoring pillar 13 and the conductive via 23.2a which ensures the connection with the active electronic element 23.1a (for example a MOS transistor whose function depends on the type of reading, by charge transfer or voltage. Reading by charge transfer: the MOS is used to transfer the charges (transfer gatef Reading in voltage: the MOS is used to amplify the electrical voltage (source followef). Finally, a support substrate 21 is assembled to the interconnection structure 22.

[0080] With reference to [Fig.3G], the stack produced is turned over, and the handle 51 is removed, then the buried oxide layer 52. This frees an upper face of the transducer 11.1, as well as that of the lateral semiconductor pads 13.1.

[0081] With reference to [Fig.3H], the thermal insulation arms 12 are produced and the production of the absorbent membrane 11 is finalized. The insulating layer 12.1, the conductive layer 12.2, and the insulating layer 12.3 are thus deposited. The conductive layer 12.2 comes into contact with the lateral semiconductor pads 13.1, as well as the p-type and n-type doped portions of the diode 11.1. Furthermore, the external connection pad (not shown) is also produced, as described previously.

[0082] With reference to [Fig.31], the absorbent membrane 11 is released by removing the sacrificial layer, here by HF vapor attack.

[0083] Thus, the method makes it possible to manufacture a detection device 1 having improved electrical performance while increasing the mechanical strength of the anchoring pillars 13 of the thermal detectors 10. In this example, the transducers 11.1 of the thermal detectors 10 are produced before the active electronic elements 23.1 insofar as they can withstand the high temperatures applied during the production of the latter.

[0084] Figures 4A and 4B illustrate different steps of a method of manufacturing a detection device 1 according to another embodiment. In this example, each thermal detector 10 comprises a reflector 24.3 of the Bragg mirror type. The Bragg mirror is then formed of a succession of thin layers of a material with a high refractive index (here silicon), distinct and spaced vertically from each other. It may comprise at least two thin layers of high index. In this example, the thermometric transducer is a junction diode, but it could be a thermistor, a transistor, etc.

[0085] With reference to [Fig.4A], we start here with a stack similar to that of [Fig.3B]. The transducer 11.1 (pn junction diode) and the lateral semiconductor pads 13.1 are made on the buried oxide layer 52. They are covered by the sacrificial layer 32. A multilayer is then made of a stack of thin layers 33.1 made of a high index material, here silicon, spaced two by two by a sacrificial layer 35 made of a mineral material, here silicon oxide. The multilayer is then structured by lithography and localized etching. Lateral vias 24.5, made here of silicon, are made at the lateral ends of the multilayer. They pass through the thin silicon layers 33.1 and are intended to ensure their retention once the sacrificial layer 35 has been removed. Finally, the thin protective layer 24.2 is deposited so as to cover the assembly, and the insulating layer 24.1 is deposited on the thin protective layer 24.2 then planarized.

[0086] With reference to [Fig.4B], the transfer and molecular bonding of the SOI substrate 40 are then carried out (see [Fig.3D]), the production of the reading structure 23 ([Fig.3E]), then that of the interconnection structure 22 ([Fig.3F]), then the production of the thermal insulation arms 12 and the finalization of the absorbent membrane 11 ([Fig.3G] and 3H), and finally the suspension of the absorbent membrane 11 by removing the sacrificial layers 32 and 35. The reflector 24.3 is thus a Bragg mirror formed of alternating Si / vacuum layers. The thin silicon layers 33.1 are kept suspended by means of the lateral vias 24.5.

[0087] Figures 5A to 5D illustrate different steps of a method of manufacturing a detection device 1 according to another embodiment. In this example, the detection device 1 comprises a second reading substrate 60, assembled to the first reading substrate 20 on the rear face and electrically connected to the latter.

[0088] With reference to [Fig.5A], we start from an assembly identical or similar to those of [Fig.2G] or 3F, except that, following the production of the interconnection structure 22, the conductive portions 22.3 of the last metallization level (lower level) are flush with one face of the stack. They are therefore not covered by a last insulating layer, and the support layer 21 of [Fig.2G] and 3F is not assembled to the stack.

[0089] With reference to [Fig.5B], a second reading substrate 60 is transferred and assembled by molecular bonding to the free face of the interconnection structure 22. The second reading substrate 60 is formed from a stack of a support substrate 61, then a reading structure 62, and finally an interconnection structure 63. The conductive portions 63.1 of the upper metallization level of the interconnection structure 63 are flush with the free face of the reading substrate 60. Thus, they are brought into contact with the conductive portions 22.3, and a hybrid oxide / oxide and metal / metal molecular bonding is produced.

[0090] With reference to [Fig.5C], the assembly is turned over, the substrate 51 and the buried oxide layer 52 are removed, so as to free an upper face of the transducer 11.1 and the lateral semiconductor pads 13.1.

[0091] With reference to [Fig.5D], the production of the thermal detector 10 is finalized by producing the thermal insulation arms 12, the absorbent membrane 11 and the external connection pad (not shown). The absorbent membrane 11 is then suspended by removing the sacrificial layer 32.

[0092] Thus, a detection device 1 is obtained comprising two reading substrates, 20 and 60, stacked and electrically connected to each other, where the two interconnection structures 22 and 63 are in contact with each other. This is made possible by the inverted configuration of the interconnection 22 and reading 23 structures in the reading substrate 20.

[0093] Particular embodiments have just been described. Different variants and modifications will appear to those skilled in the art.

Claims

1. Claims Device (1) for detecting electromagnetic radiation, comprising at least one sensitive pixel comprising a thermal detector (10), and comprising: • a reading substrate (20), comprising a reading circuit, which is formed from a stack of: • a reading structure (23) containing active electronic elements (23.1) of the reading circuit, - including at least one first active electronic element (23.1a) located in the sensitive pixel and connected to the thermal detector (10); • an interconnection structure (22) containing different metallization levels connected to the active electronic elements (23.1), - including an upper metallization level located on the side of an upper face of the reading substrate (20); • the thermal detector (10), comprising: • an absorbent membrane (11), suspended above an upper face of the reading substrate (20) and thermally insulated from it; • anchoring pillars (13), ensuring the suspension of the absorbent membrane (11) and its electrical connection to the reading circuit; • in which: • the reading structure (23) is located on and in contact with the interconnection structure (22); • the first active electronic element (23. la) is connected directly to the upper metallization level; • the anchoring pillars (13) extend continuously in the reading substrate (20) until they come into contact with the upper metallization level • characterized in that: the reading substrate (20) comprises an upper structure (24) located on and in contact with the reading structure (23), • the reading structure (23) comprising: • a first insulating layer (23.3) in which the active electronic elements (23.1) are located and through which conductive vias (23.2) extend between the active electronic elements (23.1) and conductive portions (22.1) of the upper metallization level; • a second insulating layer (23.4) which extends on and in contact with the insulating layer and the active electronic elements (23.1); • the upper structure (24) comprising: • a third insulating layer (24.1), which extends on and in contact with the second insulating layer (23.4); • a reflector (24.3) resting on the third insulating layer (24.1).

2. Detection device (1) according to claim 1, wherein the upper metallization level comprises several coplanar conductive portions (22.1), including a first conductive portion (22.1a) to which a first anchoring pillar (13) of the sensitive pixel comes into contact, and to which the first active electronic element (23.1a) is connected by means of a first conductive via (23.2a).

3. Detection device (1) according to claim 1 or 2, wherein the active electronic elements (23.1) are connected directly to coplanar conductive portions (22.1) of the upper metallization level by conductive vias (23.2), said conductive vias (23.2) and the anchoring pillars (13) being made of the same materials.

4. Detection device (1) according to any one of claims 1 to 3, in which the upper structure (24) comprises a thin protective layer (24.2), made of a material inert to hydrofluoric acid, extending above the third insulating layer (24.1), the first, second and third insulating layers (23.3, 23.4, 24.1) being made of a mineral material.

5. Detection device (1) according to any one of claims 1 to 4, wherein the reflector (24.3) is a Bragg mirror formed of several thin layers (33.1) spaced vertically from each other and held by conductive vias (24.5) passing through said thin layers (33.1).

6. Detection device (1) according to any one of claims 1 to 5, wherein the reading substrate (20) is a first reading substrate to which a second reading substrate (60) is assembled and electrically connected at a face opposite the upper face of the first reading substrate (20), the second reading substrate (60) comprising a stack of a second reading structure (62) and a second interconnection structure (63), in which: • conductive portions (63.3) of a lower metallization level of the second interconnection structure (63) are connected to active electronic elements of the second reading structure (62); • conductive portions (63.1) of an upper metallization level of the second interconnection structure (63) are in contact with conductive portions (22.3) a lower metallization level of the interconnection structure (22) of the first reading substrate (20).

7. Detection device (1) according to any one of claims 1 to 6, comprising an external connection pad (2) intended to be electrically connected to an external electronic system, extending through the reading structure (23) to come into contact with at least one conductive portion (22.1) of the upper metallization level.

8. A method of manufacturing a detection device (1) according to any one of the preceding claims, comprising the following steps: • production of a first stack comprising a handle (31; 51) on which rests a sacrificial layer (32) made of a mineral material; • transfer and molecular bonding, on the first stack, of an SOI substrate (40) formed of a silicon substrate (41), an oxide layer (42) then a thin layer of silicon (43), then removal of the silicon substrate (41); • production of the reading structure (23), the active electronic elements (23.1) being produced from the thin layer of silicon (43) on the SOI substrate (40), • production of the interconnection structure (22) on the reading structure (23), conductive portions of the upper metallization level being directly connected to the active electronic elements (23.1) by conductive vias (23.2); • turning over the stack obtained, then removing the handle (31; 51); • producing the absorbent membrane (11) on the sacrificial layer (32); • removing the sacrificial layer (32) so as to suspend the absorbent membrane (11), • the manufacturing method being such that before the molecular transfer and bonding step, a step of producing an upper structure (24), resting on the sacrificial layer (32; 52), comprising a reflector (24.3) and a thin protective layer (24.2), which are covered by a third insulating layer (24.1).

9. Manufacturing method according to claim 8, wherein the production of the reading structure (23) comprises the following steps: • deposition of a first insulating layer (23.3) covering the active electronic elements (23.1); • production of conductive vias (23.2), extending through the first insulating layer (23.3) to come into contact with the active electronic elements (23.1); • production of the anchoring pillars (13), extending through the first insulating layer (23.3) and the layer sacrificial (32) to come into contact with the handle (31; 51).

10. Manufacturing method according to claim 8 or 9, wherein the thin silicon layer (43) of the SOI substrate (40) is covered with a second insulating layer (23.4), so that, during the transfer and molecular bonding, the second insulating layer (23.4) is brought into contact with the third insulating layer (24.1).

11. Manufacturing method according to any one of claims 8 to 10, wherein, during the step of producing the absorbent membrane (11), a thermometric transducer (11.1), for example a thermistor, is produced.

12. Manufacturing method according to any one of claims 8 to 10, wherein, during the step of producing the first stack, a thermometric transducer (11.1), for example a junction diode or a transistor, is produced on the handle (31; 51), then is covered by the sacrificial layer (32).

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