Thermal detector comprising a suspended absorbent membrane with improved thermal insulation

Abstract

The invention relates to a thermal detector comprising: - a reading substrate (10) comprising a reading circuit; - an absorbent membrane (40) comprising a thermometer transducer (44) electrically connected to the reading circuit, - anchoring pillars (20) and holding arms (30) for: keeping the absorbent membrane (40) suspended above the reading substrate (10); thermally insulating the absorbent membrane from the reading substrate (10); and electrically connecting the thermometer transducer (44) to the reading circuit; the holding arms (30) being formed from a stack of at least one portion (51b; 53b) of an insulating thin film (51;53) made of a thermally insulating material, and at least one portion (52b) of a conductive thin film (52) made from an electrically conductive material. The insulating thin film (51;53) is made of amorphous boron.

Description

THERMAL DETECTOR COMPRISING A SUSPENDED ABSORBENT MEMBRANE WITH IMPROVED THERMAL INSULATION TECHNICAL FIELD

[0001] The field of the invention is that of thermal detectors of electromagnetic radiation, for example infrared or terahertz, comprising an absorbing membrane which is suspended above a reading substrate and thermally insulated from the latter. The invention applies in particular to the fields, among others, of infrared imaging, thermography, gas detection. STATE OF THE PRIOR ART

[0002] Thermal detectors may comprise an absorbing membrane, suspended above a reading substrate, comprising an absorber of the electromagnetic radiation to be detected and a thermometer transducer, for example a thermistor material, thermally coupled to the absorber.

[0003] To ensure thermal insulation of the thermometer transducer from the reading substrate, the absorbing membrane is usually suspended above the reading substrate by anchoring pillars, and is thermally insulated from it by holding arms. These anchoring pillars and holding arms also have an electrical function in that they allow the thermometer transducer to be connected to the reading circuit located in the substrate.

[0004] The holding arms may be formed by a stack of two thin insulating layers, made of a thermally and electrically insulating material, between which is located a thin conductive layer made of an electrically conductive material. This thin conductive layer is used to connect the thermometer transducer to the reading circuit. The thin insulating layers may be made of amorphous silicon deposited by chemical vapor deposition (CVD).

[0005] Figure 1 is a perspective view of an example of a thermal detector 1 according to an example of the prior art, here adapted to absorb infrared radiation from the LWIR (Long Wavelength Infrared) spectral band whose central wavelength is between approximately 8 pm and 14 pm.

[0006] The thermal detector 1 comprises an absorbent membrane 40 suspended above a reading substrate 10 by anchoring pillars 20 and thermally insulated therefrom by holding and thermal insulation arms 30. These anchoring pillars 20 and thermal insulation arms 30 also have an electrical function by electrically connecting the absorbent membrane 40 to a reading circuit located in the reading substrate 10.

[0007] The membrane 40 here comprises an absorber 47 adapted to absorb the electromagnetic radiation to be detected and a thermometer transducer in thermal contact with the absorber 47. The thermometer transducer may be a material having an electrical resistance which varies with its heating (thermistor). It may in particular be amorphous silicon or a vanadium oxide. The absorbing membrane 40 is spaced vertically from a reflector 12 by a distance so as to form a quarter-wave interference cavity optimizing the absorption by the absorber 47 of the electromagnetic radiation to be detected. Such an absorber 47 may be formed from a thin metal layer, and is generally called a Salisbury absorber.

[0008] However, it appears that a thin layer of unintentionally doped amorphous silicon, deposited by plasma-enhanced chemical vapor deposition (PECVD), may see its electrical and thermal insulation properties degraded during a subsequent heat treatment carried out for example at 400°C (for example during a step in the production of the thermistor material).

[0009] In order to improve the thermal stability of amorphous silicon, it can be deposited by thermal CVD (not plasma-assisted). To avoid having to deposit it at too high a temperature, BîHg can then be used as a catalyst for the SizH g dissociation reaction. However, it appears that boron is incorporated as a dopant in the thin layer of amorphous silicon deposited, which leads to a degradation of the electrical insulation properties. STATEMENT OF THE INVENTION

[0010] The invention aims to remedy at least in part the drawbacks of the prior art, and more particularly to propose a thermal detector with a suspended absorbent membrane, the holding arms of which have good thermal and electrical insulation properties as well as good thermal stability of these properties.

[0011] For this, the object of the invention is a thermal detector comprising: o a reading substrate, comprising a reading circuit; o an absorbent membrane, comprising a thermometer transducer electrically connected to the reading circuit, o anchoring pillars and holding arms, ensuring: the holding of the absorbent membrane suspended above the reading substrate; the thermal insulation thereof with respect to the reading substrate; and the electrical connection of the thermometer transducer to the reading circuit; the holding arms being formed from a stack of at least a portion of a thin insulating layer made of a thermally insulating material, and at least a portion of a thin conductive layer made of an electrically conductive material.

[0012] According to the invention, the thin insulating layer is made of amorphous boron.

[0013] Some preferred but not limiting aspects of this thermal detector are as follows.

[0014] The amorphous boron material of the insulating thin layer can have a thermal conductivity of at most 1.8 Wm^.K 1 , and an electrical resistivity at least equal to 2000 O. cm.

[0015] The stack of holding arms may include a portion of a lower insulating thin layer of amorphous boron, the portion of the conductive thin layer, and a portion of an upper insulating thin layer of amorphous boron.

[0016] The stack of holding arms may include a portion of a lower insulating thin layer of amorphous boron silicon aB x Yes. x and a portion of a thin upper insulating layer of amorphous boron silicon aB x Yes. x located on either side of the thin conductive layer, where x is the atomic proportion of boron in the boron silicon, preferably between 10% and 50%.

[0017] The amorphous boron insulating thin layer of the holding arms may be a lower insulating thin layer on which the conductive thin layer rests, the lower insulating thin layer and the conductive thin layer also extending into the absorbing membrane where the conductive thin layer forms two absorbing electrodes adapted to absorb the electromagnetic radiation to be detected.

[0018] The two absorbing electrodes may rest in contact with the lower insulating thin layer of amorphous boron, and have a lateral spacing of a distance less than or equal to Xc / 10, where X c is a central wavelength of a predefined spectral band AX of the electromagnetic radiation to be detected.

[0019] The thermal detector may include a portion of a thin upper insulating layer of amorphous boron, which covers the two absorbing electrodes in the membrane absorbent, and which has openings leading to the absorbent electrodes. In this case, the thermometer transducer is formed of: two end parts where the thermometer transducer comes into contact with the two absorbent electrodes through the openings in the upper insulating thin layer to form two contacts; and a central part located above the upper insulating thin layer.

[0020] An interposed insulating thin layer, made of an electrically insulating material, may be located between and in contact with the portion of the upper insulating thin layer and the central portion of the thermometer transducer, and may extend from one to the other of the two contacts.

[0021] The central part of the thermometer transducer can be suspended above the upper insulating thin layer and forms a vertical gap free of material.

[0022] The invention also relates to a method for manufacturing a thermal detector according to any one of the preceding characteristics, comprising the following steps: o providing the reading substrate; o depositing a sacrificial layer; o producing the anchoring pillars through the sacrificial layer; o producing a stack comprising at least the thin insulating layer of amorphous boron and the thin conductive layer; o localized etching of the stack so as to form the holding arms; o producing the absorbent membrane; o removing the sacrificial layer.

[0023] The thin insulating layer of amorphous boron can be produced by thermal CVD chemical vapor deposition, by injecting into a deposition chamber of a CVD reactor a precursor gas BîHg diluted in a carrier gas, the carrier gas being inert to a dissociation reaction of BîHg and chosen from argon and nitrogen, at a deposition temperature less than or equal to 400°C.

[0024] The total pressure in the deposition chamber can be between 1 Torr and 10 Torr.

[0025] The precursor gas can have a partial pressure between 1 mTorr and 100 mTorr.

[0026] The sacrificial layer can be made of a mineral material based on silicon oxide.

[0027] The process may include the following steps: o during the production of the absorbent membrane, deposition of a thin interlayer; then o production of a thermistor layer forming the thermometer transducer, the latter comprising: two end parts where it comes into contact with two absorbent electrodes; and a central part resting on and in contact with the intercalary thin layer; o when removing the sacrificial layer, the intercalary thin layer is simultaneously removed, so that the central part is suspended above the upper insulating thin layer and forms a material-free space. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 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: Figure 1, already described, is a schematic and partial perspective view of a thermal detector according to an example of the prior art; Figure 2A is a schematic and partial cross-sectional view of a thermal detector according to one embodiment; Figure 2B is a schematic and partial cross-sectional view of a thermal detector according to an alternative embodiment; Figure 2C is a schematic and partial cross-sectional view of a thermal detector according to another alternative embodiment; Figures 3A to 3H illustrate different steps of a method of manufacturing the thermal detector illustrated in Figure 2B. DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0029] 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 favor the clarity of the figures. Furthermore, the different embodiments and variants are not mutually exclusive and can be combined with each other. Unless otherwise indicated, the terms "substantially", "approximately", "of the order of" mean to within 10%, and preferably to within 5%. Furthermore, the terms "between ... and ..." and equivalents mean that terminals are included, unless otherwise stated. Finally, electrical resistivity values ​​are given for an ambient temperature of 300K.

[0030] The invention relates to a thermal detector of electromagnetic radiation, for example infrared or terahertz, in particular in the LWIR range (8-14 pm), comprising an absorbing membrane suspended above a reading substrate, and whose holding arms have good thermal insulation properties, as well as good thermal stability of these insulation properties. This thus improves the performance of the thermal detector, in particular its sensitivity.

[0031] To this end, the holding arms are formed from a stack of at least one thin insulating layer made of amorphous boron, which ensures the mechanical strength of the holding arms and has good thermal insulation properties, and at least one thin conductive layer made of an electrically conductive material, which makes it possible to electrically polarize the thermometer transducer. The thin insulating layer of amorphous boron has a thermal conductivity of at most 1.8 Wm^.K 1 , and an electrical resistivity at least equal to 2000 O. cm. In addition, these insulation properties remain good after an annealing step at a temperature for example equal to 400°C for 1 hour.

[0032] Furthermore, amorphous boron is substantially inert to the etchant (particularly hydrofluoric acid in the vapor phase) used to remove the sacrificial layer into a mineral material which can be used as a temporary support to make the absorbing membrane. The thermal detector can therefore be manufactured by implementing such a mineral sacrificial layer which can be etched with HF vapor.

[0033] Finally, amorphous boron can be deposited conformally, so that it can cover a layer with a three-dimensional topology (reliefs, steps, mesas, etc.) while maintaining sufficient thickness so that the thin layer of amorphous boron remains continuous (no material breakage).

[0034] A thin boron layer means that the thin layer consists essentially of boron atoms only. A residual atomic concentration of hydrogen is possible, but remains low (the lower the higher the deposition temperature), for example, around 5% at for a temperature of 388°C. In any case, it is not boron nitride or carbide, nor a binary compound of type B. x Yes. x , where x is the atomic proportion of boron. Furthermore, by amorphous boron, we mean that the thin layer does not contain a crystalline phase, so that the diffraction pattern, obtained by transmission electron microscopy, does not reveal a lite crystal.

[0035] Figure 2A is a schematic and partial view, in cross-section, of a thermal detector 1 according to one embodiment.

[0036] Here and for the remainder of the description, a direct three-dimensional reference frame XYZ is defined, where the XY plane is substantially parallel to the plane of a reading substrate 10 of the thermal detector 1, the Z axis being oriented in a direction substantially orthogonal to the XY plane, from the reading substrate 10 towards the absorbent membrane 40. Furthermore, the terms “lower” and “upper” are understood as relating to an increasing positioning when moving away from the reading substrate 10 in the +Z direction.

[0037] The thermal detector 1 may belong to a matrix of identical thermal detectors, preferably arranged periodically in an XY plane. Each thermal detector forms a detection pixel. The absorbent membranes then rest on the same reading substrate. In the case of infrared detection, the matrix may comprise, for example, between 60x80 and 1280x1024 pixels, with a repetition pitch of, for example, between 12pm and 8.5pm.

[0038] In this example, as described in detail below, the holding arms 30 are formed from a stack of two thin insulating layers of amorphous boron 51, 53, between which is located a thin conductive layer 52. This three-layer stack also extends into the absorbent membrane 40. Furthermore, the thin conductive layer 52 forms, at the level of the absorbent membrane 40, electrodes 41 which ensure the polarization of the thermometer transducer 44, but also the absorption of the electromagnetic radiation to be detected.

[0039] The reading substrate 10 is formed of a support substrate 11 containing the reading circuit (not shown) adapted to control and read the thermometer transducer 44. The reading circuit can be in the form of a CMOS integrated circuit. It thus comprises active microelectronic elements (for example transistors, diodes, amplifiers, etc.) and electrical interconnection levels. Here, only the upper interconnection level is shown. The interconnection levels are formed of conductive lines or portions connected vertically by conductive vias (not shown). The conductive portions and the conductive vias can be made from copper, aluminum and / or tungsten, among others, for example by means of a damascene process in which trenches made in inter-metal insulating layers. These can be made on the basis of silicon oxide (SiC, SiOF, SiOC, SiOCH...) and possibly silicon nitride SiN.

[0040] Here, conductive portions of the upper interconnection level form connection portions 13 of the anchoring pillars 20 as well as a reflector 12. The latter is adapted to reflect the electromagnetic radiation to be detected in the direction of the absorbing membrane 40, and therefore extends in the XY plane opposite the latter (and more precisely opposite the absorber located in the absorbing membrane). As indicated below, the vertical spacing between the absorbing membrane 40 (and more precisely the absorber 41) and the reflector 12 makes it possible to form a quarter-wave interference optical cavity which maximizes the absorption of the electromagnetic radiation to be detected.

[0041] A barrier layer 14, for example made of SiN, here covers the support substrate 11 and the upper interconnection line. It makes it possible to prevent the diffusion of the metal from the portions 12, 13 of the upper interconnection line towards the upcoming upper layers. Finally, a protective layer 15 here covers the barrier layer 14, and therefore also the support substrate 11 and the reading circuit (with the inter-metal insulating layers and the interconnection lines). This protective layer 15 is made of a material that is substantially inert to an etching agent used subsequently to remove the sacrificial layer(s) (for example hydrofluoric acid in the vapor phase). It can be made, for example, of AI2O3 with a thickness of approximately 20 to 40 nm, or of AIN with a thickness of approximately 100 nm.

[0042] The thermal detector 1 comprises an absorbent membrane 40, suspended above the reading substrate 10 by anchoring pillars 20, and thermally insulated from the latter by holding arms 30. The anchoring pillars 20 and holding arms 30 also provide a function of electrical connection of the thermometer transducer 44 to the reading circuit contained in the reading substrate 10.

[0043] The anchoring pillars 20 extend in the +Z direction so as to space the absorbent membrane 40 by a predefined distance from the reading substrate 10 and the reflector 12. They are made of an electrically conductive material, for example based on tungsten or copper. They are formed of a conductive via 21 each surmounted by an upper conductive pad 22, for example made of TiN with a thickness of approximately 20 to 50 nm. This pad 22 makes it possible to prevent the diffusion of the material of the conductive vias 21. Each conductive via 21 may also comprise a thin layer (not shown), extending to the periphery of the via in the XY plane and made for example of TiN, making it possible to prevent the diffusion of the material of the vias.

[0044] The holding arms 30 are formed from a stack of at least a portion of a thin insulating layer of amorphous boron, and a portion 52b of a thin conductive layer 52 made of an electrically conductive material. In this example, the stack comprises a portion 51b of a lower thin insulating layer 51 of amorphous boron, a portion 52b of a thin conductive layer 52, and a portion 53b of an upper thin insulating layer 53 of amorphous boron.

[0045] The thin insulating layers 51, 53 are made of the same material, here amorphous boron, and preferably have the same thickness. This thickness may be between 15nm and 100nm, preferably between 30nm and 70nm, for example approximately 50nm. It may be adjusted as required, depending on the width and length of the holding arms 30, so as to guarantee them good mechanical stability.

[0046] Thus, the amorphous boron of the insulating thin layers 51, 53 has a low thermal conductivity, in other words a thermal conductivity O T H at most equal to 1.8 Wm^.K 1 , thus ensuring very good thermal insulation of the absorbent membrane. The amorphous boron of the insulating thin layers 51, 53 also has an electrical resistivity p E L at least equal to 2000 O. cm. This latter property is used in particular in the absorbing membrane 40, where the two parts of the thin conductive layer 52 form polarization electrodes 41a, 41b as well as the absorber of the electromagnetic radiation to be detected. Indeed, this good electrical insulation makes it possible to reduce the lateral spacing 42 between the two parts 41a, 41b of the thin conductive layer 52, as detailed below.

[0047] Furthermore, these insulation properties are preserved following a subsequent heat treatment, for example at 400°C for at least 1 hour. In addition, the deposition of the thin insulating layers 51, 53 is a conformal deposition, so that there is no break in the continuity of the material, in particular at the level of the covering of the upper conductive pads 22, which would be likely to reduce the mechanical strength of the holding arms 30.

[0048] These insulating thin layers 51, 53 are made of amorphous boron, in the sense that they comprise substantially only boron atoms, as indicated previously. In addition, boron is amorphous and does not contain a crystalline phase. As described in detail below, they can be made by thermal CVD deposition. The electrical resistivity of the amorphous boron can be adjusted depending on the deposition operating conditions.

[0049] The conductive thin layer 52 is made of an electrically conductive material, for example TiN or NiCr, among others, with a thickness for example between 5 and 15 nm, preferably between 6 and 10 nm. It covers the lower insulating thin layer.

[0050] This three-layer stack of thin layers 51, 52, 53 also extends over the anchoring pillars 20. At the anchoring pillars 20, a portion 51a of the lower insulating thin layer 51 extends over the upper conductive pad 22. It is etched locally to allow a portion 52a of the conductive thin layer 52 to come into contact with the upper conductive pad 22. A portion 53a of the upper insulating thin layer 53 covers everything.

[0051] The absorbent membrane 40 comprises: a thermometer transducer 44, here formed by a thermistor layer, that is to say a layer made of a material whose electrical resistance varies as a function of its thermal heating; polarization electrodes 41a, 41b; and at least one absorber (here formed by the electrodes 41a, 41b) thermally coupled to the thermometer transducer. Furthermore, the absorbent membrane 40 comprises an intermediate insulating thin layer 46, made of an electrically insulating material, and located between the portion 53c of the insulating thin layer 53 and a central part 44c of the thermometer transducer 44.

[0052] The absorbent membrane 40 comprises a portion 51c, 52c, 53c of the stack of the two insulating thin layers 51, 53 and of the conductive thin layer 52. Thus, this stack extends in the XY plane to form the holding arms 30 and participate in defining the absorbent membrane 40. Here, the lower insulating thin layer 51 extends continuously in the XY plane in the holding arms 30 and the absorbent membrane 40. The portion 51c of the lower insulating thin layer 51 has a sufficient thickness to ensure good mechanical stability of the absorbent membrane 40. As for the holding arms 30, this thickness can be between 15nm and 100nm, preferably between 30nm and 70nm, for example equal to approximately 50nm.

[0053] The polarization electrodes 41a, 41b are here two distinct parts of the thin conductive layer 52. They are made of an electrically conductive material, here of a metallic material such as for example TiN or NiCr, among others, with a thickness for example between 5 and 15 nm, preferably between 6 and 10 nm.

[0054] These polarization electrodes 41a, 41b here form a thin-film absorber (Salisbury absorber). The material and thickness of the absorber are preferably chosen so that its surface resistance is substantially equal to the impedance of the vacuum.

[0055] These absorbent electrodes 41a, 41b have a large surface area in the XY plane so as to maximize the absorption of the electromagnetic radiation to be detected. They are spaced from each other in the XY plane by a distance preferably less than or equal to X c / 10, where A cis the central wavelength of the detection spectral band, here 8-14pm. Thus, this lateral spacing 42 can be of the order of approximately lpm. These two absorbing electrodes 41a, 41b remain electrically insulated due to the high electrical resistivity of the lower insulating thin layer 51 and that of the upper insulating thin layer 53 which fills the lateral space 42.

[0056] The upper insulating thin layer 53 therefore covers the absorbent electrodes 41a, 41b. It extends continuously, in the XY plane, in the holding arms 30 and the absorbent membrane 40, and has a sufficient thickness to ensure good mechanical stability of the absorbent membrane. This thickness can thus be between 15nm and 100nm, preferably between 30nm and 70nm, for example equal to approximately 50nm. The upper insulating thin layer 53 has through openings opening onto the absorbent electrodes 41a, 41b, so as to allow the thermometer transducer 44 to come into contact with the absorbent electrodes 41a, 41b: these are the contacts 43.

[0057] An intermediate insulating thin layer 46 extends over the insulating portion 53c of the insulating thin layer 53, and thus improves the electrical insulation between the electrodes 41a, 41b and the central part 44c of the thermometer transducer 44. In this example, it extends only over the part of the insulating portion 53c located between the contacts 43 in the XY plane. It extends from one to the other of the contacts 43 in the XY plane. This thin layer 46 is made of an electrically insulating material (and here resistant to HF steam) such as ALOa or AIN with a thickness for example of the order of 10 to 20 nm. This thin layer 46 makes it possible to prevent the electric current from being dissipated in the transducer 44 only in a volume located directly above the lateral spacing 42 (therefore over a distance of approximately 1 pm in the XY plane), but on the contrary that it is dissipated in the transducer 44 in a volume located between the two contacts 43 (therefore over a distance of approximately 10 pm).

[0058] The thermometer transducer 44 is here a thermistor material with a thickness for example of the order of a few tens to hundreds of nanometers. It can be a material based on a vanadium or titanium oxide, amorphous silicon, or an amorphous silicon germanium compound. Alternatively, it can also be a diode (pn or pin junction) or a field effect transistor with a metal-oxide-semiconductor structure (MOSFET), among others. Obviously, in the case of silicon germanium, vanadium or titanium oxide, as in the case of the diode or the transistor, additional layers of protection against HF steam are provided (not shown here, to favor the clarity of the figures).

[0059] It extends here over the upper insulating thin layer 53. It has two end parts 44e where it comes into contact with the absorbing electrodes 41a, 41b via the through openings (contacts 43), and a central portion 44c located between the two end portions 44e. In this example, the central portion 44c is in contact with the intermediate insulating layer 46.

[0060] The electrical resistivity of the amorphous silicon thermometer transducer 44 is for example between 600. cm and 1000. cm, for example equal to approximately 600. cm or 750. cm. The choice of electrical resistivity depends in particular on the desired reading mode, for example rolling shutter type where low resistivity is preferred, or global shutter type where high resistivity is sought. In the case of silicon germanium, the electrical resistivity is for example between 100. cm and 750. cm, for example equal to 100. cm (in the case of a rolling shutter type reading mode). The electrical resistivity can be adjusted by doping during growth, and by the atomic proportion of germanium if necessary.The thickness of such a thermometer transducer is for example between 200nm and 800nm, and depends in particular on the desired performance of the thermometer detector, depending on whether one wishes to prioritize response speed (one will choose a low thickness) or thermal resolution (one will then choose a greater thickness to minimize the noise of the detector).

[0061] Furthermore, note that the electric current flowing in such a thermometer transducer 44 depends in particular on the electrical resistivity and the thickness of the thermistor layer 44, as well as the distance separating the two contacts 43. An undesirable electric current (parasitic current) can flow from and between the ends of the absorbent electrodes 41a, 41b, through the thin insulating layers 51, 53 of amorphous boron which vertically frame the electrodes 41a, 41b. This parasitic current depends on the thicknesses and the electrical resistivity of the thin insulating layers 51, 53 of amorphous boron, as well as on the distance of the lateral spacing 42 separating the two ends of the electrodes 41a, 41b (strictly speaking the parasitic current also depends on the resistance of the electrodes 41a, 41b which act as an electrical resistance in series, but this contribution is negligible given the low electrical resistivity of TiN).We seek to ensure that this parasitic current is low, typically limited to an amplitude less than or equal to 5% of the measurement current of the electrical signal circulating in the thermistor 44.

[0062] The high electrical resistivity of the amorphous boron of the insulating thin layers 51, 53 responds favorably to this need. Indeed, for a thermal detector 1 with a pixel pitch equal to 12 pm, the distance separating the two contacts 43 is typically equal to L1 = 100 nm. Therefore, the implementation of a thermistor 44 with a resistivity equal to pl = 750 cm and a thickness equal to el = 200 nm, together with holding arms 30 formed by two insulating thin layers 51, 53 each with a thickness of 50 nm for a total thickness equal to e2 = 100 nm, requires the use of insulating thin layers 51, 53 with an electrical resistivity p2 greater than or equal to e2 = 100 nm. at 7.5xl0 3Q.cm, according to expression (1) below, if we wish to limit the distance separating the electrodes 41a, 41b to a space at most equal to L2 = lpm (equivalent to X c / 10) which makes it possible to maintain a level of absorption of infrared radiation almost similar to that of an absorber 1 L 6 unique continuous. Relation (1) is written: p 2 > — 5% x - L 2 x - exp b

[0063] However, it appears that the two thin insulating layers 51, 53 of amorphous boron of 50nm each, produced using the thermal CVD deposition process, make it possible to obtain an electrical resistivity equal to 1.7xl0 4 O.cm, therefore perfectly adequate to meet the requirement of a minimum resistivity of 7.5xl0 3O.cm. This requirement is all the better covered as the thickness el of the thermistor layer is large (with 400nm for example instead of 200nm), as the electrical resistivity pl of the thermistor is small (with 100.cm for example instead of 750.cm) or as the pixel pitch decreases (8.5pm for example instead of 12pm) and with it the distance L1 which separates the two contacts 43.

[0064] Such amorphous boron layers 51, 53 further retain high electrical resistivity after high temperature heat treatment; the electrical resistivity is still equal to l.lxl0 4 0.cm or 7.5xl0 3O.cm after a heat treatment under nitrogen carried out respectively at 380°C for 3 hours or at 400°C for 3 hours. This resilience of amorphous boron to heat treatments makes it possible to integrate the deposition steps of layers 55, 44, 46 (see fig.3F and fig.3G) without significant degradation of the resistivity which remains within the specification of relation (1).

[0065] An upper protective layer (not shown) may cover the thermometer transducer 44, to ensure protection thereof against possible contamination or degradation during the steps of the manufacturing process, such as for example the step of removing (stripping in English) the photosensitive resin used to locate the etching of the thermometer transducer 44. It may be made of an electrically insulating material, for example a dielectric material such as a silicon oxide, nitride or oxynitride, or even alumina, among others, with a thickness of a few tens of nanometers.

[0066] Thus, the thermal detector 1 has improved performance, particularly in terms of sensitivity, due to the good thermal insulation properties of the thin insulating layer 51 of amorphous boron, and here of the two thin insulating layers 51, 53 of the holding arms 30. These performances are also linked to the thermal stability of these insulation properties of the thin insulating layers 51, 53 of amorphous boron.

[0067] In addition, the lower insulating thin layer 51 forms the support layer of the absorbent membrane 40, on which the two absorbent electrodes 41a, 41b rest. The latter may have reduced lateral spacing 42 (less than or equal to X c / 10) due to the electrical resistivity of amorphous boron. Thus, the absorbing electrodes 41a, 41b can extend further over the surface of the absorbing membrane 40, and thus improve the absorption of the electromagnetic radiation to be detected.

[0068] Finally, the lower insulating thin layer 51 of amorphous boron can be deposited in a conformal manner, without material breakage, on the relief formed by the upper conductive pads 22 of the anchoring pillars 20. It can also be deposited on a mineral sacrificial layer such as silicon oxide, this with a deposition speed sufficient to be compatible with industrial requirements. Finally, the amorphous boron is substantially inert to acid etching, for example HF vapor, used to remove the mineral sacrificial layer.

[0069] Furthermore, the thermal insulation properties of a holding arm 30 can be characterized by calculating a thermal conductance per square, defined as the product of the thermal conductivity by the thickness of the arm. Such a parameter is the equivalent of the electrical resistance per square, a parameter commonly used in the field of thin films.

[0070] Thus, for a thin insulating layer 51, 53 of 50nm thickness in amorphous boron having a thermal conductivity of 1.5 Wm^.K 1 , we obtain a thermal conductance per square of 75 nW.K 1 . Similarly, for a 52nm thick conductive thin layer of TiN with a thermal conductivity of 5 Wm^.K 1 , we obtain a thermal conductance per square of 40 nW.K 1 The thermal conductance per square of a three-layer stack of two insulating thin layers 51, 53 and one conductive thin layer 52 is then 190 nW.K 1 (2x75+40).

[0071] In comparison, for a similar three-layer stack but where the insulating thin layers would be made of amorphous silicon (with thermal conductivity equal to 2.6 Wm^.K 1 ), we would obtain a thermal conductance per square of 300 nW.K 1. Also, the amorphous boron-based tri-layer stack allows to reduce the thermal conductance of the holding arms by more than 35%, thus improving the performance of the thermal detector.

[0072] It should also be noted that the holding arms 30 may be formed from a stack of thin layers comprising more than the three thin layers described previously. Thus, at least one insulating thin layer made of an amorphous boron silicon compound aB x Yes. x may also be present in the stack. Here, the parameter x corresponds to the atomic proportion of boron in the compound. It is preferably between 10% and 50%, and may be equal to approximately 30%.

[0073] Thus, the stack can comprise two thin insulating layers in aB x Yes. xarranged on either side of the conductive thin layer. These thin layers may have been deposited in the same reactor, during the deposition of the insulating thin layers of amorphous boron. The atomic proportion x is preferably identical in all the aB thin layers x Yes. x .

[0074] Thus, the stack of thin layers can be formed, in this order, from a thin layer in aB x Yes. x ; of the lower insulating layer in aB; of the thin conductive layer; of the upper insulating layer in aB; and of a thin layer in aB x Yes. x This configuration makes it possible to improve, if necessary, the adhesion of the stack on the sacrificial layer, and the adhesion of the thin intercalary layer on the stack.

[0075] Furthermore, the symmetry of such a stack makes it possible to compensate for any mechanical constraints present. A possible bimetallic effect is thus compensated, which improves the mechanical stability of the support arms and the absorbent membrane.

[0076] We can obviously consider other configurations, such as a stack of five thin layers: aB x Yes. x ; aB ; aB x Yes. x ; TiN ; aB x Yes. x ; aB ; aB x Yes. x . Here, the conductive thin layer is located in contact with two thin layers of aB x Yes. x , which makes it possible to improve, if necessary, the adhesion of the thin conductive layer, here in TiN.

[0077] Figure 2B is a schematic and partial cross-sectional view of a thermal detector 1 according to an alternative embodiment. Here, the thermal detector 1 differs from that of FIG. 2A essentially in that the thermometer transducer 44, here a thermistor material, has an empty vertical spacing 45 (free of material) with respect to the lower adjacent layer 53. The thermometer transducer 44 therefore has a bridge shape where its central part 44c is suspended above the lower adjacent layer 53.

[0078] More precisely, the thermometer transducer 44 therefore has a bridge shape, with two end portions 44e where it comes into contact with the absorbing electrodes 41a, 41b through the through openings (contacts 43), and a central portion 44c which extends continuously between the two end portions 44e. The empty vertical spacing 45 is defined at the central portion 44c of the thermometer transducer, where its lower face is spaced vertically from the upper face of the upper insulating thin layer 53 by a non-zero distance. This distance can be between 20nm and 120nm, and can be equal to approximately 50nm.

[0079] The empty vertical spacing 45 between the thermometer transducer 44 and the upper insulating thin layer 53 makes it possible to improve the electrical insulation between the central part 44c of the thermometer transducer 44 and the insulating thin layer 53, and therefore between the part 44c and the electrodes 41a and 41b. This configuration is particularly advantageous when the thin insulating layer 53 has a thickness of the order of 50nm and the electrodes 41a, 41b are spaced laterally by approximately 1pm. Furthermore, this configuration also makes it possible to reduce the mass of the absorbent membrane 40 (compared for example to FIG. 2A), and consequently makes it possible to reduce its thermal inertia (lower thermal time constant) and to increase its operating speed (for the detection of faster moving infrared scenes.

[0080] Figure 2C is a schematic and partial cross-sectional view of a thermal detector 1 according to another alternative embodiment. Here, the thermal detector 1 differs from that of FIG. 2A essentially in that the polarization electrodes 41a, 41b do not form the absorber. This is formed by a thin layer 47 deposited on the thermometer transducer 44.

[0081] The absorber 47 is located perpendicular to the lateral spacing between the two polarization electrodes 41a, 41b. Thus, the absorber 47 does not vertically cover the latter. It is therefore spaced vertically from the reflector 12 by a distance such that, taking into account the materials present in the quarter-wave cavity, the absorption is optimal for the central wavelength λ c of the detection spectral band.

[0082] Note that the insulating thin layer(s) 51, 53 made of amorphous boron can be deposited by a thermal CVD process, i.e. by a CVD deposition having thermal energy as the energy source to implement the dissociation reaction of the precursor (here BîHg). The CVD deposition is therefore not plasma-assisted. The operating conditions of deposition make it possible in particular to adjust the electrical resistivity of the amorphous boron.

[0083] The inventors have thus demonstrated that, under certain operating conditions, i.e. when the carrier gas is inert to the dissociation reaction of BiHg and the deposition temperature is at most equal to 400°C (for example between 250°C and 400°C) so as not to affect the thermal budget of the reading circuit, a thin layer of amorphous boron is deposited on the support substrate, which then has good electrical insulation and thermal insulation properties. These insulation properties remain high following a subsequent heat treatment, for example at 400°C for at least 1 hour.

[0084] The precursor gas is BiHg. It can be stored in a source, for example diluted in the carrier gas with a predefined dilution, for example here 1%. A mass flow meter allows to precisely control the feed rate of this gas mixture. For example, the feed rate can be between 0 and 1300 sccm (standard cubic centimeter per minute). As is known, the unit sccm corresponds to a unit of gas flow in cm 3 / min, at a density defined by standard conditions of temperature (0°C) and pressure (1 atm, or 760 Torr).

[0085] The carrier gas is an inert gas in the dissociation reaction of BîHg, called neutral gas. It is chosen from argon Ar and / or nitrogen N2. In this example, the carrier gas is present in a first source and ensures a first dilution of the precursor gas, here before introducing it into the reactor enclosure. The carrier gas is also present in a second source and ensures an additional dilution of the precursor gas, here in the deposition enclosure, so as to simply modify the partial pressure of the precursor gas BîHg. The carrier gas of the two sources can be identical or different. In other words, in the deposition enclosure, the precursor gas BîHg is diluted in a carrier gas which can be formed of a single chemical species (for example Ar or N2) or of several chemical species (for example Ar and N2). In any case, the carrier gas is inert in the dissociation of B2H6.It is also possible to supply the enclosure with only the carrier gas, for example during a preliminary thermalization step of the support substrate before the deposition step.

[0086] The deposition equipment is adapted to maintain the total pressure constant in the deposition chamber, both during the preliminary thermalization step and during the deposition step. This helps to improve the thickness homogeneity of the deposited thin layer.

[0087] The process for producing the thin amorphous boron layer may thus include a preliminary step of thermalizing the substrate, followed by the deposition step. Thus, during the thermalization step, the carrier gas alone is introduced into the deposition chamber. The total pressure in the chamber (thermalization pressure) may be equal to the total deposition pressure. The deposition temperature is at most 400°C, for example between 250°C and 400°C.

[0088] Then, the gas mixture formed by the precursor B2H6 diluted in the carrier gas (preferably argon Ar and / or nitrogen N2) is introduced into the deposition chamber with a predefined deposition mass flow rate. The total deposition pressure and the deposition temperature have predefined constant values.

[0089] The stack is brought to a deposition temperature of at most 400°C, and preferably between 250°C and 400°C.

[0090] The total pressure is preferably much lower than atmospheric pressure (low pressure CVD deposition), for example between 1 Torr and 10 Torr, for example between 1.4 Torr and 9 Torr. For example, the total pressure can be equal to 7 Torr. This is therefore a CVD deposition. low pressure, in the sense that the total pressure of the gas mixture in the enclosure is of the order of a few torrs, preferably at most 10 Torr, and not several tens to hundreds of torrs.

[0091] Preferably, the precursor gas BîHg is diluted in the carrier gas to 1% or less (for example to 0.1%), so that it has a partial pressure of between 1 mTorr and 100 mTorr, for example of between 1.4 mTorr and 90 mTorr.

[0092] The process allows the production of thin layers of amorphous boron with a high deposition rate, which increases from 0.5 nm / min to 50 nm / min when the deposition temperature varies from 250°C to 388°C, for a partial pressure of BiHg of 70 mTorr. It can thus be of the order of 50 nm / min, which, curiously, is almost 100 times higher than the expected deposition rate. This high deposition rate therefore makes it possible to reduce the operating time of the reactor, to reduce the consumption of gases necessary for deposition, and consequently to reduce the cost of the operation.

[0093] As examples, tests have been carried out by changing the composition of the carrier gas. Thus, a thin layer of amorphous boron is produced by injecting BiHg with a mass flow rate of 1100 sccm diluted to 1% in argon as the initial carrier gas. A second gas (diluting gas which helps to form the carrier gas), here also argon, is injected with a mass flow rate of 1000 sccm. The deposition temperature is 388°C and the total pressure is 7 Torr. The partial pressure of BiHg is therefore approximately 1100x0.01 / 2100x7 = 36.7m Torr. The thin layer of amorphous boron then has an electrical resistivity p EL equal to approximately 10.6 kO.cm, and the deposition rate is equal to 44 nm / min. In the case where the diluting gas is nitrogen also injected at 1000 sccm, the carrier gas is therefore a mixture of argon and nitrogen. Here we obtain a thin layer of amorphous boron with electrical resistivity p ELequal to approximately 10.2 kO.cm, deposited at a deposition rate of 45 nm / min. Thus, it appears that the nature of the carrier gas does not modify the properties of the deposited thin layer.

[0094] Other tests were also carried out where the partial pressure of BiHg was varied. They were carried out at a deposition temperature of 388°C, and at a total pressure of 7 Torr. The precursor gas was BiHg diluted to 1% in argon as the carrier gas, and a diluent gas, here also argon, was injected at 1000 sccm. The results are summarized in the table below. It is noted that the electrical resistivity p EL is particularly high, and increases as the partial pressure of BîHg increases.

[0095] Finally, other tests were carried out where the partial pressure of BîHg was varied, at a deposition temperature of 300°C. The total pressure remained equal to 7 Torr. The results are summarized in the table below. It is noted that the electrical resistivity p EL remains particularly high.

[0096] Figures 3A to 3H illustrate different steps of an exemplary method of manufacturing a thermal detector 1 as illustrated in Figure 2B.

[0097] With reference to Fig. 3A, the reading substrate 10 is produced. It is formed from the support substrate 11 which contains the reading circuit. Only the upper interconnection line is shown here, which notably forms the reflector 12 and connection portions 13. The barrier layer 14 made of SiN is deposited so as to cover the upper interconnection line. Then a protective layer 15 made of AI2O3 or AIN is deposited on the barrier layer 14, so as to cover the support substrate 11 (in particular the IMD layers) and the reading circuit.

[0098] With reference to Fig. 3 B, the anchoring pillars 20 are produced. For this, a sacrificial layer 54 is deposited, here made of a mineral material such as an undoped silicon oxide SiO, obtained by plasma-enhanced chemical vapor deposition (PECVD) using a TEOS precursor (tetraethyl orthosilicate). The sacrificial layer 54 covers the protective layer 15.

[0099] Through openings are then made, which pass through the sacrificial layer 54, the protective layer 15, the barrier layer 14, to open onto the connection portions 13. The anchoring pillars 20, here conductive vias 21, are made by filling the through openings with at least one metallic material, for example based on tungsten or copper. A chemical-mechanical polishing (CMP) operation is then carried out, so that the conductive vias 21 are flush with the upper face of the sacrificial layer 54. The thickness of the sacrificial layer 54 and the conductive vias 21 will make it possible to define the vertical distance between the absorbing membrane, and in particular the absorber, and the reflector 12, so as to form a quarter-wave interference cavity.

[0100] Finally, the anchoring pillars 20 are finalized by the production of upper conductive pads 22 on and in contact with the end of the conductive vias 21. For this, a thin layer of TiN with a thickness for example between 20 and 50 nm is deposited, for example by chemical or physical vapor deposition. The TiN layer is then etched locally to form the upper conductive pads 22.

[0101] With reference to FIG. 3C and FIG. 3D, a stack of a lower insulating thin layer 51, a conductive thin layer 52, and an upper insulating thin layer 53 is produced. These insulating thin layers 51, 53 are made of amorphous boron.

[0102] First of all, the lower insulating thin layer 51 of amorphous boron is deposited, with a thickness of, for example, approximately 50 nm. It can be obtained by the thermal CVD deposition process described previously. The precursor gas can be BîHg diluted to 1% in a carrier gas such as argon Ar. The gas mixture can be introduced into the deposition chamber with a flow rate of 1100 scm under a total pressure of 7 Torr, at a deposition temperature of approximately 400°C, for a duration of approximately 60 s. The lower insulating thin layer 51 is deposited conformally on the sacrificial layer 54 and on the upper conductive pads 22.

[0103] Through openings are then made through the lower insulating thin layer 51, which open onto the upper conductive pads 22. The conductive thin layer 52, here made of TiN, is then deposited, which extends over and into contact with the lower insulating thin layer 51. The conductive thin layer 52 is deposited in a conformal manner: it covers the lower insulating thin layer 51, and comes into contact with the upper conductive pads 22 through the through openings. This gives a continuous electrical connection between the anchoring pillars 20 and the conductive thin layer 52, which will form the absorbent electrodes.

[0104] Finally, the thin conductive layer 52 is locally etched, so as to form two distinct parts, physically separated from each other in the XY plane, which will form the two absorbent electrodes. These are electrically isolated from each other due to the high resistivity of the thin insulating layer 51 of amorphous boron on which they rest and are in contact. As indicated previously, this lateral spacing 42 is preferably less than or equal to Xc / 10, or here approximately lpm.

[0105] With reference to Fig. 3D, the upper insulating thin layer 53 is then deposited, preferably of the same material and thickness as the lower insulating thin layer 51. This is an amorphous boron layer with a thickness of 50nm. The operating conditions of deposit are identical or similar to those of the deposit of the lower insulating thin layer 51. A three-layer stack is thus obtained formed of the two insulating thin layers 51, 53 of amorphous boron between which the conductive thin layer 52 is located.

[0106] With reference to FIG. 3E, this three-layer stack is etched locally, so as to obtain first parts 51a, 52a, 53a located on and in contact with the upper conductive pads 22, second parts 51b, 52b, 53b which define the holding arms 30, and a third part 51c, 52c, 53c which participate in forming the absorbent membrane 40. These three parts are obviously continuously connected to each other.

[0107] With reference to Fig. 3F, a thin intercalary layer 55 is deposited, preferably sensitive to the etching agent used later when removing the sacrificial layer 54. This is therefore a second sacrificial layer. It may be an undoped silicon oxide, for example 50nm thick. This thin intercalary layer 55 is deposited conformally, and covers the upper insulating thin layer 53, and comes into contact with the sacrificial layer 54 in the openings which delimit the different parts of the three-layer stack. The thin intercalary layer 55 and the upper insulating thin layer 53 are then locally etched to lead to the absorbent electrodes 41a, 41b.

[0108] This thin intercalary layer 55 can provide a protective function for the holding arms 30 with respect to the subsequent etching steps, in particular during the formation of the thermometer transducer, so as to avoid possible degradation of the holding arms 30. It will later make it possible to obtain this vertical spacing (free of material) between the thermometer transducer and the upper insulating thin layer.

[0109] With reference to Fig. 3G, the thermometer transducer 44 is produced, here a thermistor layer. To do this, the thermistor layer is deposited on the thin interlayer 55, so that it comes into contact with the absorbent electrodes 41a, 41b through the through openings (contacts 43). The deposited layer is then locally etched to obtain the thermometer transducer, which extends only above the absorbent membrane 40.

[0110] The thermometer transducer 44 is here made of a material inert to the etching agent (HF vapor) used during the removal of the sacrificial layer 54 (and the layer 55). This may be amorphous silicon or an amorphous silicon germanium compound, among others, the electrical resistivity of which is adjusted by doping to the growth and the proportion of germanium and silicon in the compound. The thickness of the thermometer transducer may here be between 200nm and 800nm ​​approximately, depending on the performance of the thermal detector that one wishes to obtain.

[0111] With reference to Fig. 3H, the sacrificial layer 54 and the intercalary thin layer 55 are removed, here during the same HF vapor chemical etching step. This therefore results in the suspension of the absorbent membrane 40 above the reading substrate 10, as well as the suspension of the central part 44c of the thermometer transducer 44 above the upper insulating thin layer 53. This removal of the part of the intercalary thin layer 55 located under the central part 44c of the thermometer transducer is made possible insofar as the through openings (contacts 43) are separate trenches and not the same trench with a closed perimeter.

[0112] Thus, an absorbent membrane 40 is obtained suspended above the reading substrate 10, and thermally insulated from the latter in an effective manner by the holding arms 30 based on amorphous boron. The absorbent electrodes 41a, 41b can have a large surface area in the absorbent membrane 40 to the extent that their lateral spacing 42 is reduced, which is made possible by the high electrical resistivity of the thin insulating layer 51 of amorphous boron on which it rests, and by that of the upper thin insulating layer 53 which fills this lateral spacing.

[0113] Particular embodiments have just been described. Different variants and modifications will appear to those skilled in the art.

Claims

CLAIMS 1. Thermal detector (1), comprising: o a reading substrate (10), comprising a reading circuit; o an absorbent membrane (40), comprising a thermometer transducer (44) electrically connected to the reading circuit, o anchoring pillars (20) and holding arms (30), ensuring: the holding of the absorbent membrane (40) suspended above the reading substrate (10); the thermal insulation thereof with respect to the reading substrate (10); and the electrical connection of the thermometer transducer (44) to the reading circuit; • the holding arms (30) being formed from a stack of at least one portion (51b; 53b) of a thin insulating layer (51; 53) made of a thermally insulating material, and at least one portion (52b) of a thin conductive layer (52) made of an electrically conductive material; characterized in that the thin insulating layer (51; 53) is made of amorphous boron.

2. Thermal detector (1) according to claim 1, in which the amorphous boron material of the insulating thin layer (51; 53) has a thermal conductivity at most equal to 1.8 Wm -1 .K _ 1 , and an electrical resistivity at least equal to 2000 O. cm.

3. Thermal detector (1) according to claim 1 or 2, wherein the stack of holding arms (30) comprises a portion (51b) of a lower insulating thin layer (51) of amorphous boron, the portion (52b) of the conductive thin layer (52), and a portion (53b) of an upper insulating thin layer (53) of amorphous boron.

4. Thermal detector (1) according to claim 3, in which the stack of holding arms (30) comprises a portion of a lower insulating thin layer of amorphous boron silicon aB x Yes. x and a portion of a thin upper insulating layer of amorphous boron silicon aB x Yes. xlocated on either side of the thin conductive layer (52), where x is the atomic proportion of boron in the boron silicon, preferably between 10% and 50%.

5. Thermal detector (1) according to any one of claims 1 to 4, wherein the amorphous boron insulating thin layer of the holding arms (30) is a lower insulating thin layer (51) on which the conductive thin layer (52) rests, the lower insulating thin layer (51) and the conductive thin layer (52) also extending into the absorbing membrane (40) where the thin conductive layer (52) forms two absorbent electrodes (41a, 41b) adapted to absorb the electromagnetic radiation to be detected.

6. Thermal detector (1) according to claim 5, in which the two absorbing electrodes (41a, 41b) rest in contact with the lower insulating thin layer (51) of amorphous boron, and have a lateral spacing (42) of a distance less than or equal to X c / 10, where A c is a central wavelength of a predefined spectral band AÀ of the electromagnetic radiation to be detected.

7. Thermal detector (1) according to any one of claims 5 or 6: o comprising a portion (53c) of an upper insulating thin layer (53) made of amorphous boron: • covering the two absorbent electrodes (41a, 41b) in the absorbent membrane (40), and • comprising openings opening onto the absorbent electrodes (41a, 41b), o in which the thermometer transducer (44) is formed of: • two end portions (44e) where the thermometer transducer comes into contact with the two absorbing electrodes (41a, 41b) through the openings in the upper insulating thin layer (53) to form two contacts (43); and • a central part (44c) located above the upper thin insulating layer (53).

8. Thermal detector (1) according to claim 7, in which an intermediate insulating thin layer (46), made of an electrically insulating material, is located between and in contact with the portion (53c) of the upper insulating thin layer (53) and the central part (44c) of the thermometer transducer (44), and extends from one to the other of the two contacts (43).

9. Thermal detector (1) according to claim 7, wherein the central part (44c) of the thermometer transducer (44) is suspended above the upper insulating thin layer (53) and forms a vertical spacing (45) free of material.

10. A method of manufacturing a thermal detector (1) according to any one of the preceding claims, comprising the following steps: o providing the reading substrate; o depositing a sacrificial layer (54); o producing the anchoring pillars (20) through the sacrificial layer (54); o producing a first stack comprising at least the thin insulating layer (51; 53) of amorphous boron and the thin conductive layer (52); o localized etching of the first stack so as to form the holding arms (30); o production of the absorbent membrane (40); o removal of the sacrificial layer (54).

11. Manufacturing method according to claim 10, in which the thin insulating layer (51; 53) of amorphous boron is produced by thermal CVD chemical vapor deposition, by injection into a deposition chamber of a CVD reactor of a precursor gas BîHg diluted in a carrier gas, the carrier gas being inert to a dissociation reaction of BîHg and chosen from argon and nitrogen, at a deposition temperature less than or equal to 400°C.

12. Manufacturing method according to claim 10 or 11, wherein a total pressure in the deposition chamber is between 1 Torr and 10 Torr.

13. Manufacturing method according to any one of claims 10 to 12, in which the precursor gas has a partial pressure of between 1 mTorr and 100 mTorr.

14. Manufacturing method according to any one of claims 10 to 13, in which the sacrificial layer (54) is made of a mineral material based on a silicon oxide.

15. Manufacturing method according to any one of claims 10 to 14, comprising the following steps: o during the production of the absorbent membrane (40), deposition of a thin interlayer (55); then o production of a thermistor layer forming the thermometer transducer (44), the latter comprising: two end parts (44e) where it comes into contact with two absorbent electrodes (41a, 41b); and a central part (44c) resting on and in contact with the thin interlayer (55); o during the removal of the sacrificial layer (54), the thin interlayer (55) is simultaneously removed, so that the central part (44c) is suspended above the upper insulating thin layer (53) and forms a space (45) free of material.

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