DEVICE FOR DETECTING ELECTROMAGNETIC RADIATION WITH A THERMAL DETECTOR ON A RECORDING SUBSTRATE, WHICH HAS AN ACTIVE ELECTRONIC ELEMENT ARRANGED IN FRONT OF THE THERMAL DETECTOR

Description

DOMAINE TECHNIQUE

[0001] The field of the invention is that of devices for detecting electromagnetic radiation, comprising at least one thermal detector with an absorbing membrane suspended above a reading substrate and thermally insulated from it. The invention is particularly applicable to the fields of infrared or terahertz imaging, thermography, and even gas detection. ÉTAT DE LA TECHNIQUE ANTÉRIEURE

[0002] An electromagnetic radiation detection device may include sensitive pixels, each consisting of a thermal detector with a suspended absorbing membrane thermally insulated from a reading substrate. The absorbing membrane incorporates an absorber of the electromagnetic radiation to be detected, coupled with a thermometric transducer whose electrical property varies in intensity as the transducer heats up. Such a thermometric transducer may be a thermistor (for example, vanadium or titanium oxide, or even amorphous silicon), a diode (pn or pin junction), or 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. To achieve this, the absorbing membrane is typically suspended above the reading substrate by anchoring pillars and thermally insulated by thermal insulation arms. These anchoring pillars and thermal insulation arms also serve an electrical function by providing the electrical connection between the absorbing membrane and the reading circuit.

[0004] According to a so-called configuration 'above IC' (i.e., above the integrated circuit), described in particular in document EP2743659A1, the thermal detectors are implemented above the readout circuit located in the substrate. The readout circuit is in the form of a CMOS integrated circuit and includes an interconnect structure located above a readout structure.

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

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

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

[0008] However, there is a need to improve the performance of such a detection device.

[0009] Document FR 2999338A1 presents an example of the state of the art. EXPOSÉ DE L'INVENTION

[0010] The invention aims to remedy, at least in part, the drawbacks of the prior art, and more specifically to provide a detection device with improved electrical performance, particularly in terms of impulse response (limiting parasitic capacitance at the read node of the pixel's sensitive element), and even in terms of access resistance. The detection device comprises at least one thermal membrane detector suspended above a read substrate. The novel structural configuration of the read substrate not only improves the electrical performance of the detection device but also leads to better mechanical support of the anchoring pillars.

[0011] For this purpose, the object of the invention is a device for detecting electromagnetic radiation according to claim 1, comprising at least one sensitive pixel including a thermal detector, and comprising a reading substrate, including a reading circuit, which is formed of a stack of: a reading structure containing active electronic elements of the reading circuit, including at least one 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 the active electronic elements, including a top level of metallization located on the side of an upper face of the reading substrate.

[0012] The thermal detector comprises: an absorbing membrane, suspended above an upper face of the reading substrate and thermally insulated from it; and anchoring pillars, ensuring the suspension of the absorbing membrane and its electrical connection to the reading circuit.

[0013] According to the invention, the reading structure is located on and in contact with the interconnecting structure; the first active electronic element is connected directly to the upper metallization level; and the anchoring pillars extend continuously into the reading substrate until they come into contact with the upper metallization level.

[0014] The upper metallization level may include several coplanar conductive portions, including a first conductive portion with 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 anchoring pillars being made of the same materials.

[0016] The read substrate comprises a top structure situated on and in contact with the read structure. The read structure includes: 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 layer; and a second insulating layer that extends over and in contact with the insulating layer and the active electronic elements. Furthermore, the top structure includes: a third insulating layer, which extends over and in contact with the second insulating layer; and a reflector resting on the third insulating layer.

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

[0018] The reflector can be a Bragg mirror formed of several thin layers spaced vertically apart and held together by conductive vias passing through said thin layers.

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

[0020] The detection device may include 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 for manufacturing a detection device according to any one of the preceding characteristics, comprising the following steps: fabrication 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 of a silicon substrate, an oxide layer then a thin silicon layer, then removal of the silicon substrate; fabrication of the reading structure, the active electronic elements being made from the thin silicon layer on the SOI substrate; fabrication of the interconnection structure on the reading structure, the conductive portions of the upper metallization level being directly connected to the active electronic elements by conductive vias; turning over the resulting stack, then removal of the handle; fabrication of the absorbing membrane on the sacrificial layer; removal of the sacrificial layer so as to suspend the absorbing membrane.

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

[0023] The process may include, before the molecular transfer and bonding step, a step of creating a top structure, based 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 molecular transfer and bonding, the second insulating layer is brought into contact with the third insulating layer.

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

[0026] Alternatively, during the first stacking stage, a thermometric transducer, for example a junction diode or a transistor, can be made on the handle and then covered by the sacrificial layer. BRÈVE DESCRIPTION DES DESSINS

[0027] Other aspects, objectives, advantages, and features of the invention will become clearer upon reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which: there figure 1A is a schematic and partial cross-sectional view of a detection device according to an embodiment where the reading substrate comprises a reading structure located on the interconnection structure; the figure 1B is a schematic and partial cross-sectional view of a detection device according to a variant embodiment; the figures 2A à 2H illustrate different stages of a manufacturing process for a detection device identical or similar to that of the fig.1A ; THE figures 3A à 3I illustrate different stages of a manufacturing process for a detection device identical or similar to that of the fig.1B ; THE figures 4A et 4B illustrate different stages of a manufacturing process for a detection device similar to that of the fig.1B , where the reflector is a Bragg mirror; the figures 5A à 5D illustrate different stages of a manufacturing process for a detection device similar to that of the fig.1B where a second reading substrate is assembled and connected on the back side to the first reading substrate. EXPOSÉ DÉTAILLÉ DE MODES DE RÉALISATION PARTICULIERS

[0028] In the figures and throughout the description, the same reference numerals represent identical or similar elements. Furthermore, the various elements are not drawn to scale to ensure clarity. Moreover, the different embodiments and variants are not mutually exclusive and may be combined. Unless otherwise stated, the terms "approximately," "around," and "in the order of" mean within 10%, and preferably within 5%. Furthermore, the terms "between ... and ..." and equivalents mean inclusive of the bounds, unless otherwise specified.

[0029] The invention relates to a device for detecting electromagnetic radiation, for example infrared or terahertz radiation. The detection device can thus be particularly adapted to detect infrared radiation in the LWIR range ( Long Wavelength Infrared, (in English) whose wavelength is between approximately 8µm and 14µm.

[0030] The detection device comprises at least one sensitive pixel, and preferably an array of sensitive pixels. A sensitive pixel consists of a thermal detector, designed to absorb electromagnetic radiation, and electrically connected to a readout circuit located in the substrate on which it rests.

[0031] The thermal detector is of the absorbing 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 absorbing membrane to the reading circuit. The absorbing membrane incorporates a temperature-sensing transducer, that is, an element whose electrical properties change with temperature. Such a transducer can be a thermistor based on vanadium or titanium oxide, or even amorphous silicon. It can also be a pn or pin junction diode, or a MOSFET.

[0032] The readout substrate consists of a stack of an interconnect structure (BEOL type) and a readout structure (FEOL type). Each sensitive pixel includes at least one active electronic element from the readout structure (e.g., a MOS transistor), connected to the thermal detector via the upper metallization layer of the interconnect structure. Furthermore, the interconnect structure provides the electrical connection of the sensitive pixels to other active electronic elements of the readout circuit, as well as to an external connection pad.

[0033] The interconnection levels are each formed of coplanar conductive sections, which are connected to those of adjacent interconnection levels by conductive vias. The interconnection structure therefore comprises several parallel interconnection levels arranged vertically. It includes a first, or upper, interconnection level located on the side of the thermal detector, intermediate interconnection levels, and a final, or lower, interconnection level located on the side opposite the thermal detector.

[0034] According to the invention, in the readout substrate, the readout structure is located on top of the interconnection structure. 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 prior art detection devices, where the FEOL-type readout structure is located below the BEOL-type interconnection structure.

[0035] Furthermore, the first active electronic element of the sensitive pixel (for example, the MOS transistor) is connected directly to the upper metallization level, that is, 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.

[0036] Finally, the anchoring pillars extend continuously into the reading substrate until they reach the upper metallization layer. By "extend continuously," we mean that the anchoring pillars extend without any discontinuity from their constituent materials to the upper metallization layer. The anchoring pillars therefore have a lower portion located within the reading substrate, which improves their mechanical strength.

[0037] Also, within the same sensitive pixel, the anchoring pillars and the first active electronic element are in contact with the top metallization line. This structural configuration improves the electrical performance of the detection device, as access resistance and parasitic capacitances are reduced, while simultaneously strengthening the mechanical strength of the anchoring pillars.

[0038] There figure 1A is a schematic and partial cross-sectional view of a detection device 1 according to an embodiment. In this example, the transducer 11.1 is a thermistor.

[0039] We define here and for the rest of the description a direct three-dimensional orthogonal XYZ frame, where the XY plane is substantially parallel to the principal plane of the reading substrate 20, and where the Z axis is oriented in the direction of the absorbing membrane 11. In the rest of the description, the terms "lower" and "upper" are understood as being relative to an increasing positioning when moving away from the reading substrate 20 along the +Z direction.

[0040] The reading substrate 20 here comprises a stack consisting of a support substrate 21, an interconnection structure 22 (BEOL), a reading structure 23 (FEOL), and finally here a top structure 24 which includes a reflector 24.3.

[0041] The support substrate 21 is an optional substrate on which the interconnection structure 22 rests and is in contact. It is a handle that was used during the manufacturing process (cf. fig.2A à 2H ). Here, it is a silicon substrate, for example several hundred microns thick.

[0042] The interconnect structure 22 is part of the reading substrate 20, which comprises a plurality of parallel metallization levels. Each metallization level has coplanar conductive portions connected to the conductive portions of 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 in pairs. The interconnect structure 22 provides the electrical connection, for each sensitive pixel, between the absorbing membrane 11 and the active electronic element(s) 23.1 associated with the absorbing membrane 11.It also provides the electrical connection of each sensitive pixel to any other reading system adapted to read 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 base of the column (in the case where the transducer is a thermistor), this CTIA being also connected to one or more thermal compensation detectors. Finally, it provides the electrical connection to an external connection pad 2 (see . fig.2H ).

[0043] The metallization levels thus comprise, along the -Z direction, a first metallization level, or upper metallization level, formed by the conductive portions 22.1, located on the upper face of the reading substrate 20, and a final metallization level, or lower metallization level, formed by the conductive portions 22.3, located on 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 therefore understood that there are no metallization levels of the interconnect structure 22 located above the upper level, that is, 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 can be made, for example, of copper, aluminum, or tungsten, among other materials. The insulating layers 22.5 are made of a mineral material, for example, based on silicon oxide or silicon nitride.

[0044] The readout structure 23 is part of the readout substrate 20 and includes the active or passive electronic components connected to the sensitive pixels, or even to one or more compensation pixels. The active electronic components 23.1 can be transistors or diodes (e.g., photodiodes, light-emitting diodes), and the passive electronic components can be capacitors, resistors, etc. The readout structure 23 is located above the interconnection structure 22 along the vertical Z-axis; that is, it is situated between the upper surface of the readout substrate 20 and the interconnection structure 22.

[0045] For each sensitive pixel, the active electronic elements 23.1 are connected to the upper metallization level, specifically to the conductive portions 22.1, via conductive vias 23.2. The active electronic elements 23.1 are located below the absorbing membrane 11 in the XY plane and above the upper metallization level. The active electronic elements 23.1 are directly connected to the conductive portions 22.1 by the conductive vias 23.2; that is, each conductive via 23.2 is in contact with both 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 specified, when two elements are referred to as being directly connected, it is understood that they are connected by a conductive via, without passing through an intermediate metallization level.

[0046] Other active electronic elements 23.1 are located at the base of the column, notably 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 top face and the interconnect structure 22.

[0047] 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 parasitic capacitances.

[0048] The conductive vias 23.2 of the active electronic elements 23.1, directly connecting the latter to the upper metallization level, can be made of the same material(s) as those of the anchoring pillars 13. By way of example, the conductive vias 23.2 can 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 (cf. fig.2C à 2E ), made, for example, from silicon, and are surrounded by one or more insulating layers 23.3 and 23.4 of a dielectric material. In this example, the active electronic elements 23.1 are located in an insulating layer 23.3 and are covered by an insulating layer 23.4. This insulating layer 23.4 is made of an oxide and is bonded by oxide-to-oxide molecular bonding to an insulating layer 24.1 also made of an oxide. This transfer and molecular bonding step is described later with reference to the fig. 2D .

[0049] 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 extends here over and in contact with the insulating layer 24.1. It is adapted to ensure protection of the reading substrate 20 against chemical attack, for example in an acidic HF (hydrofluoric acid) medium, implemented to etch the sacrificial mineral layer(s) used in the fabrication 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 Al 2 O 3, or even of aluminum nitride or fluoride, and can have a thickness of between a few tens and a few hundred nanometers, for example between 10nm and 500nm.

[0050] The reflector 24.3 is adapted to reflect the light radiation to be detected towards the absorbing membrane 11. It is located below the membrane in the XY plane, and forms with it a quarter-wave interference optical cavity, allowing the absorption of the light radiation by the absorbing membrane 11 to be maximized. In this example, the reflector 24.3 is on and in contact with the protective thin film 24.3, but it is possible to make it in contact with the insulating layer 24.1 and to cover it with the protective thin film 24.2. It can be made of at least one silicon layer a few hundred nanometers thick, heavily doped with a doping level of at least 10< 19 < cm -3 < .

[0051] The thermal detector 10 includes an absorbing membrane 11, suspended above the reading substrate 20 by thermal insulation arms 12 and anchoring pillars 13. The absorbing membrane 11 incorporates the temperature transducer 11.1, here a thermistor. The thermal insulation arms 12 and the anchoring pillars 13 are electrically conductive and provide the electrical connection of the thermistor 11.1 to the reading circuit. The absorbing membrane 11 and the thermal insulation arms 12 are components known to those skilled in the art. In this example, the arms 12 and the absorbing membrane 11 are formed by stacking 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 (to absorb 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 8 nm to 15 nm so as to obtain a layer resistance of approximately 377 Ω / square.

[0052] The anchoring pillars 13 can be made of a shell, for example, of Ti / TiN or Ta / TaN, and a core, for example, of Cu and / or W. They extend vertically along the Z-axis to the thermal insulation arms 12, and each comes into contact with a conductive portion 22.1 of the upper metallization layer. They also pass through the thin protective layer 24.2, the insulating layer 24.1, and 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 layer. By "extend continuously," we mean here that there is a continuity of material in 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 that would be located above the upper metallization level.Thus, each anchoring pillar 13 has a lower portion that 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). Furthermore, 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.

[0053] Thus, by arranging the reading structure 23 on the interconnection structure 22, and by ensuring that the anchoring pillars 13 extend continuously until they contact the conductive portions 22.1 of the upper metallization layer, 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 layer, and in particular to one of them (22.1a) with which one of the anchoring pillars 13 is in contact. This improves both the mechanical strength of the anchoring pillars 13 and reduces access resistance and parasitic capacitances. The electrical performance of the detection device 1 is thereby improved, for example, in terms of impulse response and reading speed.Furthermore, as detailed later, this configuration allows for the simple implementation of manufacturing processes for the detection device 1, which differ from each other in particular in that the transducer 11.1 can, or cannot, withstand the high temperatures (around 1000°C) of the fabrication of the active electronic elements 23.1. In the example of the . fig.1A , transducer 11.1 is a thermistor which cannot withstand these high temperatures.

[0054] There figure 1B This is a schematic, partial cross-sectional view of a detection device 1 according to one embodiment. In this example, the transducer 11.1 is a diode (which can withstand the high temperatures, on the order of 1000°C, required for the fabrication 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 a pn semiconductor junction at the level of the absorbing membrane 11. The diode 11.1 is made of silicon, preferably single-crystal. The absorbing membrane 11 has a lower insulating layer 11.3 (passivation), on which the diode 11.1 rests and is in contact. A stack of an insulating layer 12.1, a conductive layer 12.2, and an upper insulating layer 12.3 rests on the diode 11.1. At the level of the absorbing membrane 11, the conductive layer 12.2 comes into contact with the p-type and n-type doped portions of diode 11.1, and ensures their electrical bias. Here, it extends above diode 11 and forms an absorbing layer of the light radiation to be detected.

[0055] THE figures 2A à 2H illustrate different stages of a manufacturing process for a detection device 1 identical or similar to that of the fig.1A In this example, the reflector 24.3 is made of a material that can withstand the high temperatures of the active electronic components 23.1, and is therefore manufactured before them. Conversely, the thermistor 11.1 cannot withstand these high temperatures, and is therefore manufactured after the active electronic components 23.1.

[0056] With reference to the 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 fabrication of the absorbing membrane 11. Its thickness will define the distance of the quarter-wave optical cavity between the absorbing membrane 11 and the reflector 24.3.

[0057] With reference to the fig.2B Next, the reflector 24.3 and then the protective thin layer 24.2 are fabricated. This is done by depositing a continuous layer 33 of over-doped silicon onto and in contact with the sacrificial layer 32. The reflector 24.3 is then fabricated by lithography and localized etching of the silicon layer 33. Openings 34 are formed in the silicon layer 33 to allow for the subsequent fabrication of the anchoring pillars 13. The protective thin layer 24.2 is then deposited conformally, so as to continuously cover the reflector 24.3 and extend down 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 to cover the protective thin layer. Planarization is then performed. This stacking 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.

[0058] With reference to the fig.2C The process involves bonding a SOI 40 substrate (silicon substrate 41, buried oxide layer 42, and then a thin silicon layer 43, preferably single-crystal) to the insulating layer 24.1. This bonding is a molecular oxide-to-oxide bond. To achieve this, an insulating layer 23.4, made of an oxide, is first deposited onto the thin silicon layer 43. The insulating layers 23.4 and 24.1 are then brought into contact to ensure molecular bonding.

[0059] With reference to the fig.2D The silicon substrate 41 is removed (the buried oxide layer 42 can be at least partially retained), and then the active electronic elements 23.1 and 23.1a are fabricated (lithography, etching, deposition, doping, etc.). During these steps, a high temperature, on the order of 1000°C, can be applied. However, the reflector 24.3 is made of a material that can withstand these high temperatures. An insulating layer 23.3 made of a dielectric material, in this case an oxide, is then deposited to cover the active electronic elements 23.1 and 23.1a. Finally, the anchoring pillars 13 and the conducting vias 23.2 are fabricated. These are 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.

[0060] With reference to the fig.2E The interconnection structure 22 is then fabricated, starting with the upper metallization level, followed by the intermediate metallization levels, and finally the lower metallization level. Specifically, 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. These elements are thus directly connected to the upper metallization level. Furthermore, a similar conductive portion 22.1a of the upper metallization level is in contact with an anchoring pillar 13 and a conductive via 23.2a, which provides the connection to the active electronic element 23.1a, in this case, an injection-mode MOSFET. Finally, a support substrate 21 is assembled to the interconnection structure 22.

[0061] With reference to the fig.2F The stack 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 made on the sacrificial layer 32. The thermal insulation arms 12 are in contact with one end of the anchoring pillars 13 which were made beforehand.

[0062] With reference to the fig.2G The external connection pad 2 is formed 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 made of at least one metallic layer, deposited in a notch formed through the sacrificial layer 32, the thin protective layer 24.2, and the underlying insulating layers.

[0063] With reference to the fig.2H The absorbent membrane 11 is released by removing the sacrificial layer 32, here by chemical etching with HF vapor phase. The external connection pad 2 may have a peripheral upper portion 2b that extends laterally, preferably by at least 5 µm, from the vertical portion 2a. Thus, during HF vapor etching, an unetched portion of the sacrificial layer 32 can be located below the peripheral upper portion 2b, thereby strengthening the mechanical strength of the external connection pad 2.

[0064] Thus, the manufacturing process 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 process, the thermistor 11.1 is sensitive to the high temperatures generated during the fabrication of the active electronic components 23.1, which explains why it is manufactured after them.

[0065] THE figures 3A à 3I illustrate different stages of a manufacturing process for a detection device 1 identical or similar to that of the fig.1B This process differs from that of the fig.2A à 2H essentially in that the thermometric transducer 11.1 is a pn junction diode made before the readout structure 23. Several steps are identical or similar to those of the process of fig.2A à 2H and are therefore only described briefly.

[0066] With reference to the fig.3A , we provide a substrate SOI 50, formed of a silicon substrate 51, a buried oxide layer 52, then a thin layer of silicon 53 preferably single-crystal.

[0067] With reference to the fig.3B The thermometric transducer 11.1, here a pn junction diode, is fabricated from the silicon thin film 53. To achieve this, the silicon thin film 53 is structured by lithography and localized etching, and the p-type and n-type doped portions are fabricated by localized ion implantation. Lateral semiconductor pads 13.1, formed from the silicon thin film 53 and preferably doped, can be fabricated and are intended to be located at the top of the anchoring posts 13. Furthermore, a passivation thin film 11.3 can be deposited so as to cover only the transducer 11.1.

[0068] With reference to the fig.3C A sacrificial layer 32, made of a mineral material, for example silicon oxide, is deposited to cover the transducer 11.1, the lateral semiconductor pads 13.1, and the buried oxide layer 52. The thickness of this sacrificial layer 32 defines the dimensions of the quarter-wave optical cavity between the absorbing membrane 11 and the reflector 24.3. The reflector 24.3 is then fabricated, followed by the thin protective layer 24.2, and finally the insulating layer 24.1, in a manner identical or similar to that described in reference to the fig.2B .

[0069] With reference to the fig.3D , we transfer and glue a substrate SOI 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, to the insulating layer 24.1. The bonding here is a molecular oxide / oxide bond.

[0070] With reference to the fig.3E , substrate 41 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, on the order of 1000°C, which however does not alter the properties of the transducer 11.1 or that of the reflector 24.3.

[0071] Finally, the anchoring pillars 13 and the conductive vias 23.2 are fabricated. 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 protective thin 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 performed.

[0072] With reference to the fig.3F The interconnection structure 22 is constructed, 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, a similar conductive portion 22.1a of the upper metallization level is in contact with an anchoring pillar 13 and the conductive via 23.2a which provides the connection with the active electronic element 23.1a (for example, a MOS transistor whose function depends on the type of readout, by charge transfer or voltage. Readout by charge transfer: the MOS is used to transfer the charges ( transfert gate ) . Voltage reading: the MOS is used to amplify the electrical voltage ( source follower ) .Finally, a support substrate 21 is assembled to the interconnection structure 22.

[0073] With reference to the fig.3G , we turn over the stack made, and we remove the handle 51 and then the buried oxide layer 52. We thus free up a top face of the transducer 11.1, as well as here that of the lateral semiconductor pads 13.1.

[0074] With reference to the fig.3H The thermal insulation arms 12 are made and the absorption 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. In addition, the external connection pad (not shown) is also made, as described previously.

[0075] With reference to the fig.3I , the absorbing membrane 11 is released by removing the sacrificial layer, here by HF vapor attack.

[0076] Thus, the process makes it possible to manufacture a detection device 1 with 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 made before the active electronic elements 23.1 insofar as they can withstand the high temperatures applied during the manufacture of the latter.

[0077] THE figures 4A et 4B illustrate different stages of a manufacturing process for a detection device 1 according to another embodiment. In this example, each thermal detector 10 includes a Bragg mirror-type reflector 24.3. The Bragg mirror is then formed of a succession of thin layers of a high-refractive-index material (here, silicon), distinct and vertically spaced from one another. It can comprise at least two high-index thin layers. In this example, the thermometric transducer is a junction diode, but it could be a thermistor, a transistor, etc.

[0078] With reference to the fig.4A Here, we start with a stacking similar to that of the fig.3B The transducer 11.1 (pn junction diode) and the lateral semiconductor pads 13.1 are fabricated on the buried oxide layer 52. They are covered by the sacrificial layer 32. A multilayer is then fabricated, consisting of a stack of thin films 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 fabricated at the lateral ends of the multilayer. They pass through the silicon thin films 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 whole, and the insulating layer 24.1 is deposited on the thin protective layer 24.2 and then planarized.

[0079] With reference to the fig.4B , then the transfer and molecular bonding of the SOI 40 substrate are carried out (cf. fig.3D ), the realization of reading structure 23 ( fig.3E ), then that of the interconnection structure 22 ( fig.3F ), then the construction of the thermal insulation arms 12 and the finalization of the absorbent membrane 11 ( fig.3G And 3H ), and finally the suspension of the absorbing membrane 11 by removing the sacrificial layers 32 and 35. The reflector 24.3 is thus a Bragg mirror formed by alternating layers of Si / vacuum. The thin silicon layers 33.1 are held suspended by means of the lateral vias 24.5.

[0080] THE figures 5A à 5D illustrate different stages of a manufacturing process for 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.

[0081] With reference to the fig.5A we start from a set identical or similar to those of the fig.2G Or 3F except that, following the construction of the interconnection structure 22, the conductive portions 22.3 of the lowest metallization level (lower level) are flush with one face of the stack. They are therefore not covered by a final insulating layer, and the support layer 21 of the fig.2G And 3F is not assembled to the stack.

[0082] With reference to the 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 by 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 achieved.

[0083] With reference to the fig.5C , we turn the whole thing over, we remove the substrate 51 as well as the buried oxide layer 52, so as to free up a top face of the transducer 11.1 and the lateral semiconductor pads 13.1.

[0084] With reference to the fig.5DThe thermal detector 10 is finalized by fabricating 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.

[0085] Thus, we obtain a detection device 1 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 structures 22 and 23 in the reading substrate 20.

[0086] Specific embodiments have just been described. Different variations and modifications will be apparent to those skilled in the art.

Claims

1. A device (1) for detecting an electromagnetic radiation, comprising at least one sensitive pixel including a thermal detector (10), and including: ∘ a readout substrate (20), including a readout circuit, which is formed of a stack of: • a readout structure (23) containing active electronic elements (23.1) of the readout 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 readout substrate (20); ∘ the thermal detector (10), including: • an absorbing membrane (11), suspended above an upper face of the readout substrate (20) and thermally insulated from the latter; • anchor pillars (13), ensuring suspension of the absorbing membrane (11) and the electrical connection of the latter to the readout circuit; ∘ wherein: • the readout structure (23) is located over and in contact with the interconnection structure (22); • the first active electronic element (23.1a) is directly connected to the upper metallization level; • the anchor pillars (13) continuously extend in the readout substrate (20), with no discontinuity in the materials which form them, until coming into contact with the upper metallization level; ∘ the readout substrate (20) including: • an upper structure (24) located over and in contact with the readout structure (23), ∘ the readout structure (23) including: • a first insulating layer (23.3) in which the active electronic elements (23.1) are located and throughout 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), made of oxide, which extends over and in contact with the insulating layer and the active electronic elements (23.1); ∘ the upper structure (24) including: • a third insulating layer (24.1), made of oxide, which extends over and in contact with the second insulating layer (23.4), the second and third layers being bonded one to the other by molecular bonding; • a reflector (24.3) resting on the third insulating layer (24.1).

2. The detection device (1) according to claim 1, wherein the upper metallization level includes several coplanar conductive portions (22.1), including a first conductive portion (22.1a) with which a first anchor 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. The detection device (1) according to claim 1, wherein the active electronic elements (23.1) are directly connected to coplanar conductive portions (22.1) of the upper metallization level through conductive vias (23.2), said conductive vias (23.2) and the anchor pillars (13) being made of the same materials.

4. The detection device (1) according to claim 1, wherein the upper structure (24) includes a protective thin layer (24.2), made of a material inert to hydrofluoric acid, extending over 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. The detection device (1) according to claim 1, wherein the reflector (24.3) is a Bragg mirror formed of several thin layers (33.1) spaced vertically apart from one another and held by conductive vias (24.5) crossing said thin layers (33.1).

6. The detection device (1) according to claim 1, wherein the readout substrate (20) is a first readout substrate to which a second readout substrate (60) is assembled and electrically connected at the level of a face opposite to the upper face of the first readout substrate (20), the second readout substrate (60) including a stack of a second readout structure (62) and of a second interconnection structure (63), wherein: ∘ conductive portions (63.3) of a lower metallization level of the second interconnection structure (63) are connected to active electronic elements of the second readout 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) of a lower metallization level of the interconnection structure (22) of the first readout substrate (20).

7. The detection device (1) according to claim 1, including an outer connection pad (2) intended to be electrically connected to an outer electronic system, extending throughout the readout structure (23) so as to come into contact with at least one conductive portion (22.1) of the upper metallization level.

8. A method for manufacturing a detection device (1) according to claim 1, including the following steps: ∘ making a first stack including a handle (31; 51) on which a sacrificial layer (32) made of a mineral material rests; ∘ transferring and molecular bonding, onto the first stack, of a SOI substrate (40) formed of a silicon substrate (41), an oxide layer (42) then a silicon thin layer (43), then removal of the silicon substrate (41); ∘ making the readout structure (23), the active electronic elements (23.1) being made starting from the silicon thin layer (43) over the SOI substrate (40), ∘ making the interconnection structure (22) over the readout structure (23), conductive portions of the upper metallization level being directly connected to the active electronic elements (23.1) through conductive vias (23.2); ∘ turning obtained stack over, then removing the handle (31; 51); ∘ making the absorbing membrane (11) over the sacrificial layer (32); ∘ eliminating the sacrificial layer (32) so as to suspend the absorbing membrane (11).

9. The manufacturing method according to claim 8, wherein making of the readout structure (23) includes the following steps: ∘ depositing a first insulating layer (23.3) covering the active electronic elements (23.1); ∘ making conductive vias (23.2), extending throughout the first insulating layer (23.3) so as to come into contact with the active electronic elements (23.1); ∘ making the anchor pillars (13), extending throughout the first insulating layer (23.3) and the sacrificial layer (32) so as to come into contact with the handle (31; 51).

10. The manufacturing method according to claim 8, including, before the transferring and molecular bonding step, a step of making an upper structure (24), resting on the sacrificial layer (32; 52), including a reflector (24.3) and a protective thin layer (24.2), which are covered with a third insulating layer (24.1).

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

12. The manufacturing method according to claim 8, wherein, during the step of making the absorbing membrane (11), a thermometric transducer (11.1), for example a thermistor, is made.

13. The manufacturing method according to claim 8, wherein, during the step of making the first stack, a thermometric transducer (11.1), for example a junction diode or a transistor, is made over the handle (31; 51), then is covered with the sacrificial layer (32).