Device for detecting electromagnetic radiation and manufacturing process

Abstract

Title: Electromagnetic Radiation Detection Device and Manufacturing Method. The invention relates to an electromagnetic radiation detection device (1), comprising at least one detector disposed within a cavity (2) formed by an encapsulation structure, said encapsulation structure comprising anchoring pillars (21), at least one of which is connected to at least one detector, and support pillars (22) surmounting said anchoring pillars (21). Advantageously, the support pillars (22) have a portion (220) extending over at least one flank (210) of the anchoring pillars (21). The invention also relates to a manufacturing method for such a device (1). Figure for the abstract: Fig. 9A

Description

Title of the invention: Device for detecting electromagnetic radiation and manufacturing method Technical field

[0001] The field of the invention is that of devices for detecting electromagnetic radiation, in particular infrared or terahertz, comprising at least one thermal detector, for example a micro-bolometer, encapsulated in a cavity. The invention applies in particular to the field of infrared or terahertz imaging, thermography, presence detection, or even gas detection. STATE OF THE ART

[0002] Devices for detecting electromagnetic radiation, for example infrared or terahertz, may comprise a matrix of thermal detectors each comprising a membrane capable of absorbing the electromagnetic radiation to be detected and containing a thermometric transducer such as a thermistor material. To ensure thermal insulation of the thermometric transducers from the reading substrate on which the detectors are manufactured, the absorbing membranes are usually suspended above the substrate by means of anchoring pillars and are thermally insulated from them by thermal insulation arms. These anchoring pillars and thermal insulation arms also have an electrical function by connecting the absorbing membranes to the reading circuit generally arranged in the substrate.

[0003] To ensure optimal operation of thermal detectors, a low pressure level may be required. For this, thermal detectors are generally confined, or encapsulated, alone or in groups, in at least one hermetic cavity under vacuum or at reduced pressure.

[0004] Among the various techniques used to encapsulate thermal detectors (integration in a hermetic housing, hermetic assembly with a second substrate, confinement by thin film deposition), a hermetic cavity delimited with the reading substrate by an encapsulation structure formed of thin films is a technique particularly suited to the high-volume, low-cost manufacture of radiation detection devices.

[0005] Document FR2003858 describes an example of such an encapsulation method for manufacturing a detection device 1, illustrated here in [Fig.l], whose thermal detectors are arranged in a cavity 2 formed within an encapsulation structure on the reading substrate 100. The method uses two mineral sacrificial layers to successively produce the thermal detectors connected to the anchoring pillars 21, then the upper part of the encapsulation structure. These sacrificial layers are then removed by chemical vapor etching. The upper part of the encapsulation structure is formed by a thin layer 23 called encapsulation and by a thin layer 24 called sealing intended to close vents 230 used to remove the sacrificial layers. The encapsulation layer 23 here extends continuously above the thermal detectors and on the surface of an unetched portion of the second sacrificial layer. It also extends continuously in vertical portions to form support pillars 22 of the encapsulation structure which are positioned resting on the anchoring pillars 21. An electrically insulating layer 3 is further provided between the anchoring pillars 21 and the support pillars 22, to electrically insulate the thermal detectors supported by the anchoring pillars 21.

[0006] The support pillars of the encapsulation structure have the particular function of maintaining the mechanical integrity of the encapsulation structure which is subjected to the forces of atmospheric pressure external to the cavity. The support pillars are therefore designed to withstand compressive forces. A disadvantage of this solution is that the layer at the interface between the support pillars and the anchor pillars does not have strong adhesion with the anchor pillars. Consequently, if the encapsulation structure is subjected to a tensile force, the support pillars may become detached from the anchor pillars. Such tensile forces may typically be induced by differential mechanical stresses existing between the reading substrate and the encapsulation structure.

[0007] There therefore remains a need to have a method for manufacturing an encapsulation structure with improved mechanical strength. One objective of the invention is to meet this need.

[0008] In particular, an object of the invention is a detection device making it possible to improve the mechanical strength of the encapsulation structure, in particular limiting the risk of detachment between support pillars of the encapsulation structure and anchoring pillars supporting the detectors. Another object of the invention is a method for producing such a device.

[0009] Other objects, features and advantages of the present invention will become apparent from the following description and accompanying drawings. It is understood that other advantages may be incorporated. SUMMARY

[0010] To achieve this objective, according to one embodiment, a device for detecting electromagnetic radiation is provided, comprising at least one detector arranged within a cavity formed by an encapsulation structure, said encapsulation structure comprising anchoring pillars, at least one of which is connected to the other at least one detector, and support pillars surmounting said anchor pillars.

[0011] Advantageously, the support pillars have a portion extending over at least one flank of the anchoring pillars.

[0012] This makes it possible to increase the contact surface of the support pillars with the underlying structure. The adhesion force is thus improved. Furthermore, the support pillars are at least partially in direct contact with the anchor pillars, via the portion extending on the flank of the anchor pillars. This direct contact offers an adhesion force that is typically greater than indirect contact via an electrical insulation layer interposed between the anchor pillars and the support pillars, as disclosed by document FR2003858. The mechanical strength is further improved.

[0013] In the context of the development of the present invention, it has in fact been found that the electrical insulation layer, typically formed by a stack of thin layers, could delaminate or detach from the anchoring pillar under the effect of a tensile force linked to the presence of a differential mechanical stress between the reading substrate and the encapsulation structure. Delamination of the insulation layer is all the more likely when it comprises a large number of layers of different nature and of small thicknesses.

[0014] To improve the adhesion of the layers to each other and avoid delamination, a person skilled in the art could consider optimization solutions, for example by modifying the nature of the layers of the insulation layer, or by improving the preparation of the surfaces and / or the methods of deposition of these different layers. These routine solutions are typically accessible to a person skilled in the art. However, they remain relatively ineffective and have not been retained in the context of the present invention.

[0015] The original connection between the anchoring pillars and the support pillars according to the invention thus advantageously makes it possible to significantly improve the mechanical strength of the encapsulation structure of the electromagnetic radiation detection device.

[0016] Another aspect of the invention relates to a method of manufacturing such a device for detecting electromagnetic radiation, comprising: - Providing a substrate, - Form a first sacrificial layer on said substrate, - Form the anchor pillars through said first sacrificial layer, - Place at least one detector above the first sacrificial layer and forming a connection between the at least one detector and at least one anchor pillar among the anchor pillars, - Form a second sacrificial layer on the first sacrificial layer, on the at least one detector and on the anchor pillars, - Forming a second opening in said second sacrificial layer above the anchor pillars, said second opening extending over at least one flank of the anchor pillars, and preferably extending into the first sacrificial layer, - Filling said second opening with at least one filling material so as to form the support pillars surmounting the anchor pillars, - Forming an encapsulation layer of an encapsulation material on the second sacrificial layer and at least partly on the support pillars, - Form at least one vent within the encapsulation layer, said vent opening onto the second sacrificial layer, - Removing the second and first sacrificial layers through the at least one vent, so as to form a cavity around the at least one detector, - Forming a sealing layer of a sealing material on the encapsulation layer so as to seal the at least one vent, and preferably so as to make the cavity airtight. BRIEF DESCRIPTION OF THE FIGURES

[0017] The aims, objects, as well as the characteristics and advantages of the invention will emerge more clearly from the detailed description of an embodiment thereof which is illustrated by the following accompanying drawings in which:

[0018] [Fig.l] [Fig.l] is a device for detecting electromagnetic radiation comprising an encapsulation structure, according to the prior art.

[0019] [Fig.2A][Fig.3A][Fig.4A][Fig.5A][Fig.6A][Fig.7A][Fig.8A][Fig.9A] Figures nA (n=2...9) schematically illustrate, according to a first cross-section, the steps of manufacturing a device for detecting electromagnetic radiation, according to an embodiment of the present invention.

[0020] [Fig.2B][Fig.3B][Fig.4B][Fig.5B][Fig.6B][Fig.7B][Fig.8B][Fig.9B] Figures nB (n=2...9) schematically illustrate, according to different cross-sections, the manufacturing steps illustrated in the corresponding figures nA, according to an embodiment of the present invention.

[0021] [Fig.lOA][Fig.llA][Fig.l2A] Figures jA (j=10... 12) schematically illustrate, according to a first transverse section, the steps of manufacturing a device for detecting electromagnetic radiation, according to another embodiment of the present invention.

[0022] [Fig.lOB][Fig.llB][Fig.l2B] Figures jB (j=10... 12) schematically illustrate in a cross-section the manufacturing steps illustrated in the corresponding figures jA, according to another embodiment of the present invention.

[0023] [Fig.l3A][Fig.l3B][Fig.l3C][Fig.l3D] Figures 13A to 13D illustrate diagram technically in top view of manufacturing variants of a device for detecting electromagnetic radiation, according to different embodiments of the present invention.

[0024] [Fig.l4A][Fig.l4B] Figures 14A and 14B schematically illustrate a device for detecting electromagnetic radiation according to another embodiment of the present invention. [Fig.l4B] corresponds to the transverse section XX illustrated in [Fig.l4A].

[0025] [Fig. 15] [Fig. 15] schematically illustrates in top view a manufacturing variant of a device for detecting electromagnetic radiation, according to an embodiment of the present invention.

[0026] For the cross-sectional figures, section planes are indicated (AA, BB, ..., XX) with cross-references to the section planes of the corresponding figures. The drawings are given as examples and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily to the scale of practical applications. In particular, in the principle diagrams, the thicknesses and / or dimensions of the different layers, patterns and reliefs are not representative of reality. For reasons of clarity, a single support pillar surmounting a single anchor pillar is shown in each figure. It is understood that the detection device typically comprises a plurality of support pillars and anchor pillars. DETAILED DESCRIPTION

[0027] Before beginning a detailed review of embodiments of the invention, optional features which may possibly be used in combination or alternatively are set out below:

[0028] According to one example, the device further comprises an intermediate structure between the support pillars and the anchoring pillars, said intermediate structure having: - an isolation arm configured to support the at least one detector, and - at least one overhang around an upper face of the anchoring pillars.

[0029] According to one example, the portion of the support pillars passes around the at least one overhang or through the at least one overhang. Thus, the portion of the support pillars comes into contact with the side of the anchoring pillars under the overhang, passing around or through the overhang. The mechanical anchoring of the support pillars is thus done under the overhang. The overhang contributes to the mechanical strength of the support pillars. The mechanical strength of the encapsulation structure is reinforced.

[0030] According to one example, the portion of the support pillars comprises a first part at the level of the at least one overhang having a first dimension La in a reference direction x or y, and a second part beyond the at least one overhang on at least one flank of the anchor pillars and having a second dimension Lb along said reference direction x or y, such that the second dimension Lb is strictly greater than the first dimension La. The portion of the support pillars thus widens at the flank of the anchor pillars, after passing at the overhang. The second widened part thus forms a stop against the overhang preventing traction of the support pillars with respect to the anchor pillars.

[0031] According to one example, the portion of the support pillars forms an assembly key, for example a dovetail or a tooth, with the at least one overhang of the intermediate structure. The portion of the support pillars is engaged with the overhang. It may be in the form of an embedding with the overhang or more generally a mechanical assembly taking advantage of the overhang.

[0032] According to one example, at least the second part of the portion of the support pillars is in contact with at least one flank of the anchor pillars.

[0033] According to one example, the first and second parts of the portion of the support pillars are in contact with at least one flank of the anchor pillars. The adhesion of the portion of the support pillars with the anchor pillars is improved.

[0034] According to one example, the first part of the portion of the support pillars is in contact with the upper face of the anchor pillars. The adhesion of the portion of the support pillars with the anchor pillars is further improved.

[0035] According to one example, the portion of the support pillars extends over a first flank of the anchor pillars, located on a first side, and extends over a second flank of the anchor pillars, located on a second side opposite the first side. The mechanical strength is further reinforced.

[0036] According to one example, the cavity is closed by an encapsulation layer of an encapsulation material resting on the support pillars, and by a sealing layer of a sealing material on said encapsulation layer, and the support pillars are at least partly formed by the encapsulation layer alone or by the encapsulation layer and the sealing layer, so that the support pillars comprise the encapsulation material alone or the encapsulation material and the sealing material.

[0037] According to one example, the cavity is delimited laterally by a peripheral wall extending substantially vertically between the reading substrate and the encapsulation layer. This peripheral wall is typically based on the material of the sacrificial layers used for the formation of the cavity, typically based on SiO2.

[0038] According to one example, the cavity is hermetic.

[0039] According to one example, the cavity has a height less than or equal to 10 pm, or even less than 5 pm (for example if only vacuum packaging function is required).

[0040] According to one example, the thin encapsulation layer has a thickness less than or equal to 800 nm.

[0041] According to one example, the support and / or anchoring pillars are arranged in a matrix manner.

[0042] According to one example, the thermal detectors comprise an absorbent membrane suspended above the reading substrate by the anchoring pillars.

[0043] According to one example, the method further comprises, after formation of the first sacrificial layer and before formation of the second sacrificial layer, formation of an intermediate structure between the support pillars and the anchoring pillars, said intermediate structure having: - an isolation arm configured to support the at least one detector, said isolation arm forming the connection between said at least one detector and the at least one anchoring pillar among the anchoring pillars, - at least one overhang around an upper face of the anchoring pillars.

[0044] According to one example, the formation of the second opening comprises - An anisotropic etching configured to extend the second opening under and in line with the at least one overhang, - An isotropic etching configured to extend the second opening under the at least one overhang and against the at least one flank of the anchoring pillars, such that, after filling said second opening, the portion of the support pillars has a first part at the level of the at least one overhang having a first dimension La in a reference direction x or y, and a second part below the at least one overhang on the at least one flank of the anchoring pillars and having a second dimension Lb in said reference direction x or y, such that the second dimension Lb is strictly greater than the first dimension La.

[0045] According to one example, the method further comprises, after forming the intermediate structure, forming a first opening in the intermediate structure, said first opening partially exposing the upper face of the anchoring pillars and passing through the at least one overhang around the perimeter of the anchoring pillars.

[0046] According to one example, the formation of the second opening in the second sacrificial layer is configured so that said second opening passes at least partly through the first opening. Thus, during subsequent filling, the portion of the support pillars is directly in contact with the upper face of the anchor pillars and the flank of the anchor pillars, crossing the overhang. This reinforces the mechanical strength and the adhesion of the support pillars to the anchor pillars.

[0047] According to one example, the filling of the second opening is at least par- initially carried out during the formation of the encapsulation layer, by conformal deposition of said encapsulation layer on the second sacrificial layer and in the second opening, so that the at least one filling material comprises the encapsulation material. This makes it possible to limit the number of steps required for filling and encapsulation layer formation, which can thus be carried out at least partly simultaneously.

[0048] According to one example, the filling of the second opening is at least partially carried out during the formation of the sealing layer, by depositing said sealing layer on the encapsulation layer, so that the at least one filling material comprises the encapsulation material and the sealing material. This makes it possible to limit the number of steps necessary for the filling and the formation of the sealing layer, which can thus be carried out at least partly simultaneously.

[0049] According to one example, the filling of the second opening is carried out before the formation of the encapsulation layer, by a filling material different from the encapsulation material. This makes it possible to choose a filling material according to its adhesion properties, independently of its optical properties.

[0050] According to one example, the filling material is chosen to be identical to or based on the material of the anchor pillars.

[0051] Unless incompatibility exists, it is understood that all of the above optional features may be combined to form an embodiment that is not necessarily illustrated or described. Such an embodiment is obviously not excluded from the invention. The features and advantages of one aspect of the invention, for example the device or the method, may be adapted mutatis mutandis to the other aspect of the invention.

[0052] The invention relates generally to an electromagnetic radiation detection device adapted to detect infrared or terahertz radiation, and a method of manufacturing such a device. The detection device comprises at least one detector, preferably an array of thermal detectors located in a hermetic cavity. The array of thermal detectors forms a preferably periodic array. Each of the thermal detectors is an optically sensitive detector, and forms a detection pixel adapted to detect the electromagnetic radiation of interest.

[0053] In the context of the present invention, the cavity is delimited in its lower part by the reading substrate and in its upper part by an encapsulation structure which comprises one or more thin layers transparent to the electromagnetic radiation to be detected, including in particular a thin encapsulation layer and a thin layer for sealing the vents. The encapsulation structure comprises in in addition to anchor pillars and support pillars surmounting the anchor pillars, all of these pillars providing support for the upper layers of the encapsulation structure.

[0054] The cavity is further delimited laterally by a peripheral wall which extends continuously around the matrix of thermal detectors. As explained below, the peripheral wall typically corresponds to an unetched portion of the sacrificial layers.

[0055] By thin layer is meant a layer formed by microelectronic material deposition techniques, the thickness of which is preferably less than or equal to 10 qm. Furthermore, a thin layer is said to be transparent when it has a transmission coefficient greater than or equal to 50%, preferably 75%, or even 90% for a central wavelength of the spectral range of the electromagnetic radiation to be detected.

[0056] It is specified that, in the context of the present invention, the terms "on", "overcomes", "covers", "underlying", "facing" and their equivalents do not necessarily mean "in contact with". Thus, for example, the deposition, transfer, bonding, assembly or application of a first layer on a second layer does not necessarily mean that the two layers are in direct contact with each other, but means that the first layer at least partially covers the second layer by being either directly in contact with it, or by being separated from it by at least one other layer or at least one other element.

[0057] A layer may also be composed of several sub-layers of the same material or of different materials.

[0058] A substrate, a film, a layer, “based” on a material A, is understood to mean a substrate, a film, a layer comprising this material A only or this material A and possibly other materials, for example doping elements or alloying elements.

[0059] Several embodiments of the invention implementing successive steps of the manufacturing method are described below. Unless explicitly stated, the adjective “successive” does not necessarily imply, even if this is generally preferred, that the steps follow one another immediately, intermediate steps being able to separate them.

[0060] Furthermore, the term “step” means the carrying out of a part of the method, and can designate a set of sub-steps.

[0061] Furthermore, the term "step" does not necessarily mean that the actions carried out during a step are simultaneous or immediately successive. Certain actions of a first step may in particular be followed by actions linked to a different step, and other actions of the first step may be repeated subsequently. Thus, the term stage does not necessarily mean unitary and inseparable actions in time and in the sequence of phases of the process.

[0062] The term “selective etching with respect to” or “etching having selectivity with respect to” means etching configured to remove a material A or a layer A with respect to a material B or a layer B, and having an etching rate of the material A greater than the etching rate of the material B. The selectivity is the ratio between the etching rate of the material A and the etching rate of the material B. It is noted SA:B. A selectivity SA:b of 10:1 means that the etching rate of the material A is 10 times greater than the etching rate of the material B.

[0063] A preferably orthonormal reference frame, comprising the x, y, z axes, is shown in the attached figures. When a single reference frame is shown on the same sheet of figures, this reference frame applies to all the figures in this sheet.

[0064] In the present patent application, we will preferably speak of thickness for a layer or a film, and of height for a device or a structure. The thickness is taken along a direction normal to the main extension plane of the layer or film. Thus, a layer or a film typically has a thickness along z. The encapsulation structure or the pillars have a height along z. The relative terms “on”, “surmounts”, “under”, “underlying” refer to positions taken along the z direction. A “lateral” dimension corresponds to a dimension along a direction of the xy plane. A “lateral” or “laterally” extension is understood to mean an extension along one or more directions of the xy plane.

[0065] An element located "perpendicular to" or "in line with" another element means that these two elements are both located on the same line perpendicular to a plane in which a lower or upper face of a substrate mainly extends, that is to say on the same line oriented vertically in the cross-sectional figures.

[0066] 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 the limits are included, unless otherwise stated.

[0067] Figures 2A to 9A illustrate, according to a first sectional view (AA, CC, ..., OO), an embodiment of a device for detecting infrared radiation between 8 pm and 14 pm wavelengths, containing thermal detectors of the micro-bolometer type. Figures 2B to 9B illustrate this same embodiment according to other sectional views BB, DD, ..., PP illustrated in the corresponding Figures 2A to 9A.

[0068] As illustrated in Figures 2A, 2B, the first steps consist of forming in a known manner anchoring pillars 21 on a substrate 100 preferably comprising a reading circuit based on CMOS transistors (acronym meaning Complementary Metal Oxide Semiconductor), called the reading substrate 100. The reading circuit of the substrate 100 typically comprises at least one metallization level comprising conductive portions 101, generally made of Cu, flush with the surface of the substrate 100. These conductive portions 101 are here intended to electrically connect the anchoring pillars 21 to the reading circuit of the substrate 100.

[0069] On this reading substrate 100, a copper diffusion barrier layer 110, for example made of silicon nitride (SiN) can be formed. A protective layer 120, for example made of aluminum nitride (AIN) or aluminum oxide (A12O3), electrically insulating and chemically inert with respect to hydrofluoric acid (HF), is then formed. This layer 120 has the function of protecting the substrate 100 during a subsequent step of chemical etching by HF vapor configured to remove the sacrificial layers and form the cavity of the device.

[0070] A first sacrificial layer 20a, preferably made of silicon dioxide (SiO2), is then formed on the protective layer 120. This first sacrificial layer 20a is then opened by localized etching, by means of photolithography patterns corresponding to the location of the anchoring pillars 21 above the portions 101. The shape of the photolithography patterns, which may be circular, square or rectangular, substantially defines the section in the xy plane of the anchoring pillars 21. The etching is extended through the layers 120, 110 so as to expose the conductive portion 101. A step of depositing a barrier layer (not shown), for example made of TiN, is preferably carried out before filling the openings of the first sacrificial layer 20a with a step of depositing a layer of an electrically conductive material, for example made of Tungsten (W) or Copper (Cu).A chemical-mechanical polishing (CMP) step aimed at removing the materials deposited on the upper face of the first sacrificial layer 20a and forming the upper face 211 of the anchoring pillars 21 is then carried out. At this stage, the anchoring pillars 21 are formed in the form of metal pads typically having a dimension along x and / or y or a diameter of the order of 0.5 μm, and a height along z of the order of 1.8 μm. These anchoring pillars 21 are electrically connected to the reading circuit of the substrate 100. The upper face 211 of the anchoring pillars 21 is substantially in the plane of the upper face of the first sacrificial layer 20a. The upper face 211 may form a small depression with respect to the upper face of the first sacrificial layer 20a, resulting from the CMP polishing operation which preferentially removes the metallic material of the anchoring pillar 21 with respect to the SiO2 of the sacrificial layer 20a.This depression is for example of the order of 70 nm, which represents less than 4% of the height of a 1.8 pm anchoring pillar. The flank(s) 210 of the anchoring pillars 21 are in contact with the first sacrificial layer 20a.

[0071] As illustrated in Figures 3A, 3B, a wafer 310, for example circular, octagonal, square or rectangular, is formed on the upper face 211 of each metal pad 21. This wafer 310 is advantageously made of TiN to act as a barrier to the diffusion of the metal atoms of the metal pad. It has a thickness typically between 20 nm and 50 nm. It typically has a dimension along x and / or y or a diameter greater than that of the anchoring pillar 21. It is preferably centered with respect to the anchoring pillar 21. It thus forms a first overhang with respect to the anchoring pillar 21. The wafer 310 projects laterally from the anchoring pillar 21 over a distance of a few tens to a few hundreds of nanometers. This first overhang can extend over a distance greater than or equal to 50 nm, for example 100 nm or 200 nm.

[0072] As illustrated in Figures 4A, 4B, a stack of layers 301, 302, 303 is formed on the wafer 310 and on the upper face of the first sacrificial layer 20a, then structured by etching so as to form an intermediate structure 3 comprising a thermal insulation arm 30. The intermediate structure 3 thus comprises the wafer 310 and the structured stack of layers 301, 302, 303. This intermediate structure 3 is intended to be interposed between the underlying anchoring pillar 21, and a support pillar above.

[0073] The thermal insulation arm 30 is generally narrow with a width along y of, for example, between 0.1 μm and 0.3 μm, typically 0.18 μm. The thermal insulation arm 30 here comprises an electrically conductive layer 302 made of TiN, with a thickness of approximately 7 nm, interposed between two dielectric layers 301, 303 made of amorphous silicon (a-Si), each having a thickness typically of between 15 nm and 50 nm. At a central zone of the wafer 310, the layer 301 is removed before deposition of the layer 302 so that the conductive layer 302 is electrically connected to the anchoring pillar 21. In a known manner, the thermal insulation arm 30 is intended to support an absorbent membrane (not illustrated) capable of absorbing infrared radiation. This absorbent membrane may typically include a thermometric transducer such as a thermistor capable of measuring the temperature of the absorbent membrane.As is known, the membrane and the thermistor form a thermal detector called a micro bolometer.

[0074] The structuring of the stack of layers 301, 302, 303 is configured so as to keep a portion of these three layers 301, 302, 303 straddling the wafer 310 and on the periphery of the wafer 310. This makes it possible to obtain a mechanical and electrical connection between the thermal insulation arm 30 and the anchoring pillar 21. This portion of the stack of the three layers 301, 302, 303 advantageously extends laterally beyond the periphery of the wafer 310, partly on the first sacrificial layer 20a. This lateral extension is typically of the order of 0.2 μm. It makes it possible to form an overhang 31 of the intermediate structure 3. The overhang 31 of the intermediate structure 3 forms an overhang with respect to the flank 210 of the anchoring pillar 21, over a lateral distance typically between 0.4 pm and 0.6 pm.

[0075] After formation of the intermediate structure 3, the thermal detector is typically formed at the end of the thermal insulation arm 31, as described in document FR2999805. The thermal detector typically forms a micro-bolometer comprising an absorbent membrane and a thermometric transducer connected to the anchoring pillar 21.

[0076] As illustrated in Figures 5A, 5B, after formation of the intermediate structure 3, a first opening 300 is made in the stack of layers 301, 302, 303, 310. This opening 300 is typically made by photolithography and etching. The shape of the opening 300, in the xy plane, can be square, rectangular, circular, oblong or other. This opening 300 can be made by an etching capable of simultaneously etching the layers 301, 302, 303, 310 based on amorphous silicon a-Si and titanium nitride TiN, selectively to the material of the metal pad of the anchoring pillar 21. Such an etching can be obtained by a RIE etching process (reactive ion etching) using fluorinated chemical agents. The etching parameters will be able to be adjusted without difficulty by those skilled in the art.

[0077] As illustrated in [Fig.5A], the opening 300 is preferably made at an overhang 31, straddling the upper face 211 of the anchoring pillar 21. A portion of the upper face 211 of the anchoring pillar 21 is thus advantageously exposed. This exposed portion of the anchoring pillar 21 will subsequently advantageously make it possible to form direct contact with the support pillar, thus improving the adhesion between the support pillar and the anchoring pillar 21. The opening 300 here extends directly above the first sacrificial layer 20a. The lateral extension along y of the opening 300 above the first sacrificial layer 20a may be of the order of 0.2 μm to 0.4 μm. The lateral extension along y of the opening 300 above the anchoring pillar 21 may be of the order of 0.1 pm to 0.2 pm. This makes it possible to maintain a sufficient contact surface between the metal stud 21 and the intermediate structure 3.

[0078] In [Fig.5A], the opening 300 extends along y on the first sacrificial layer 20a beyond the overhang 31. The continuity along x of the overhang 31 is thus interrupted. The opening 300 straddles the intermediate structure 3. According to another possibility not illustrated, a peripheral part of the overhang 31 may remain around the opening 300. The continuity along x of the overhang 31 is preserved for this peripheral part. The opening 300 is in this case internal to the intermediate structure 3. It opens in all cases onto the first sacrificial layer 20a, and preferably onto the upper face 211 of the anchoring pillar 21.

[0079] As illustrated in [Fig.5B] which is a section along the plane HH illustrated in the [Fig.5A], the opening 300 is preferably made in the middle of the overhang 31, while retaining parts 31a, 31b of the overhang 31 (along y). These parts 31a, 31b of the overhang 31 will subsequently advantageously form a support for the support pillar, opposing traction along +z.

[0080] As illustrated in Figures 6A, 6B, a second sacrificial layer 20b is first formed on the first sacrificial layer 20a, on the intermediate structure 3 and on the thermal detectors. The second sacrificial layer 20b is preferably of the same nature as the first sacrificial layer, here made of SiO2. The second sacrificial layer 20b is then opened locally by etching above the anchoring pillars 21. This second opening 200 is typically produced by an etching capable of etching the second sacrificial layer 20b selectively to the materials of the intermediate structure 3 and the metal pad of the anchoring pillar 21.This second opening 200 extends laterally in line with the overhangs 31 of the intermediate structure 3, and vertically over the entire height of the second sacrificial layer 20b, so as to expose the part of the upper face 211 of the anchoring pillar 21 previously exposed by the formation of the first opening 300. Advantageously, the second opening 200 is extended along the flank 210 of the anchoring pillar 21, here in the first sacrificial layer 20a, by an opening portion 201a located under the overhang 31, against the flank 210 of the anchoring pillar 21. This opening portion 201a is typically formed by anisotropic etching along z through the first opening 300. The etching can be done by RIE having a plasma chemistry based on fluorinated species.In this case, the etching parameters will be adjusted so that the respective etching rates of the SiO2 of the first and second sacrificial layers 20a, 20b on the one hand, and of the amorphous silicon of the layers 303, 301 are sufficiently distinct. Typically, the etching parameters will be adjusted so as to obtain an SSiO2:a selectivity greater than 20:1, preferably greater than 50:1, for example of the order of 80:1. At this stage, the second opening 200, 201a here makes it possible to expose the part of the upper face 211 of the anchoring pillar 21 and a part of the flank 210 of the anchoring pillar 21. According to one possibility, the second opening 200, 201a can be filled to form the support pillar as illustrated below. The support pillar then has a part in contact with the upper face 211 of the anchor pillar 21 and the flank 210 of the anchor pillar 21. The adhesion of the support pillar to the anchor pillar 21 is already improved.

[0081] According to a preferred possibility illustrated in Figures 7A, 7B, the second opening 200 is widened by an isotropic etching process, for example by wet etching based on a partially diluted aqueous solution of buffered HF. This isotropic etching makes it possible to extend the second opening 200 under the overhanging parts 31a, 31b not etched during the formation of the first opening 300. This opening extension 201b thus makes it possible to uncover a larger surface area of ​​the flank 210 of the anchoring pillar 21. The support pillar subsequently formed in this opening 200, 201b thus has direct contact with the larger anchoring pillar 21. Furthermore, the opening extension 201b advantageously extends under and against the overhanging portions 31a, 31b. The support pillar subsequently formed in this opening 200, 201b thus advantageously abuts against the overhanging portions 31a, 31b. The support pillar thus forms an embedment with the intermediate structure 3. The mechanical tensile strength along +z is further improved.

[0082] As illustrated in Figures 8A, 8B, the filling of the second opening 200, 200b to form a support pillar surmounting the anchor pillar 21.

[0083] According to this embodiment, an electrically insulating and HF-inert layer 231, for example a layer of A12O3, is first deposited in the second opening and on the surface of the second sacrificial layer 20b. The layer 231 can be deposited by ALD (Atomic Layer Deposition). A deposition of the ALD type makes it possible to obtain a conformal deposition of the layer 231 of A12O3. The layer 231 thus has a substantially constant thickness, typically between 20 nm and 40 nm. This layer 231 has the function of electrically insulating the support pillar from the intermediate structure 3 and the anchoring pillar 21, electrically connected to the thermal detectors. Photolithography and etching steps make it possible to remove the layer 231 of A12O3 deposited on the upper face of the second sacrificial layer 20b. A portion of the layer 231 located at the edge of the openings, on the upper face of the second sacrificial layer 20b, can be preserved.This part can typically extend from 250 nm to 500 nm.

[0084] An encapsulation layer 23 made of amorphous silicon is then deposited conformally in the second opening, on the layer 231 and on the surface of the second sacrificial layer 22b. The encapsulation layer 23 may have a uniform thickness of between 200 nm and 800 nm. The deposition of this encapsulation layer 23 made of amorphous silicon may be made with a thickness sufficient to partially or completely fill the second opening, in particular at the level of the opening extension in contact with the underlying anchoring pillar 21. This encapsulation layer 23 continuously forms the upper part of the encapsulation structure and at least partly the support pillar of the encapsulation structure.

[0085] As illustrated in Figures 9A, 9B, vents 230 are first etched through the encapsulation layer 23. These vents 230 open onto the second sacrificial layer 20b. A chemical attack in HF vapor is then carried out to remove the two sacrificial layers 20a, 20b in SiO2, through the vents 230. A cavity 2 is thus formed. A sealing layer 24 is then formed to seal the vents 230, and optionally to complete the filling of the second opening. In this embodiment, the support pillar 22 is formed simultaneously with the formation of the encapsulation layer 23 and the formation of the sealing layer 24. This saves a process step dedicated to filling the second opening for the formation of the support pillar 22. The support pillar 22 here comprises the encapsulation material and optionally the sealing material.

[0086] The sealing layer 24 is typically formed by a secondary vacuum deposition technique such as vacuum evaporation deposition of the material to be deposited. The cavity 2 is thus sealed under reduced pressure. This allows optimal operation of thermal detectors such as micro-bolometers housed within the cavity 2. The sealing layer 24 is made of a sealing material transparent to the radiation that it is desired to detect, for example germanium (Ge) for a detection device in the infrared range. An antireflection layer 25, here made of zinc sulfide (ZnS), is preferably deposited on the surface of the sealing layer 24 to improve the transmission of infrared radiation through the assembly of the two layers 24, 25. A detection device 1 comprising an encapsulation structure around a hermetic cavity 2 is thus formed.The encapsulation structure comprises a support pillar 22 comprising a lower portion 220 in contact with the underlying anchor pillar 21. In this example, the portion 220 of the support pillar 22 comprises a first part 220a passing through the overhang 31, and a second part 220b under the overhang 31. The first part 220a is in contact with the upper face of the anchoring pillar 21. This improves the adhesion of the support pillar 22 to the anchoring pillar 21. The second part 220b is in contact with the flank 210 of the anchoring pillar 21. This further improves the adhesion of the support pillar 22 to the anchoring pillar 21. The first part 220a has a first dimension La along x, and the second part 220b has a second dimension Lb along x strictly greater than the first dimension La. This makes it possible to form a stop for the portion 220 against the overhang 31.The mechanical tensile strength of the support pillar 22 on the anchor pillar 21 is further improved.

[0087] In the following, different variants of the device 1 and of the manufacturing method are described and illustrated. Only the characteristics which differ from the first embodiment are described and illustrated. The other characteristics are deemed identical to those of the first embodiment.

[0088] As illustrated in Figures 10A, 10B, according to one possibility, the filling of the second opening and the formation of the encapsulation layer are carried out separately. The filling of the second opening can be done with one or more filling materials different from the encapsulation material. The layer encapsulation layer no longer extends here within the support pillar 22. The encapsulation layer can be produced at a later stage, after formation of the support pillars, and in a material different from that used for the support pillars. This embodiment makes it possible to independently choose the materials used to form, on the one hand, the support pillars, and on the other hand, the encapsulation layer. This embodiment advantageously makes it possible to form support pillars of the encapsulation structure in a material offering good adhesion with the material of the anchoring pads. The encapsulation layer can be produced in optically transparent materials, for example in amorphous silicon for a radiation detector between 8 and 14 pm in wavelength.

[0089] The support pillars 22 may be made of tungsten like the anchor pillars 21. This makes it possible to obtain good adhesion between the support pillar 22 and the anchor pillar 21. According to one possibility, a layer 40 of chromium is previously deposited in a conformal manner in the second opening. This layer 40 of chromium is in direct contact with the exposed parts of the anchor pillars 21. This layer 40 of chromium may have a thickness of between 100 nm and 200 nm. A thick deposit of tungsten, for example with a thickness of between 200 nm and 800 nm, then makes it possible to fill the second opening. The support pillar 22 may thus comprise a relatively thin layer 40 of chromium and a thick part 41 of tungsten. The chromium layer 40 here has the function of further improving the adhesion between the anchoring and support pillars 21, 22.The support pillar 22 can therefore be made of materials chosen for their adhesion properties, independently of their optical properties. In this embodiment, the support pillar 22 does not necessarily comprise materials transparent to the radiation to be detected. Furthermore, in this embodiment, the support pillar 22 does not necessarily comprise an electrically insulating and HF-inert layer because the electrical insulation between the encapsulation layer and the intermediate structure 3 and the anchoring pillar 21 can advantageously be formed at a later stage. Indeed, providing such an electrical insulation layer between the anchoring pillar 21 and the support pillar 22 can degrade the adhesion properties which are sought here.

[0090] Chemical mechanical polishing (CMP) is typically performed to remove materials deposited on the upper face of the second sacrificial layer 20b and to form the upper face 221 of the support pillars 22. The upper face 221 of the support pillars 22 is here substantially in the plane of the upper face of the second sacrificial layer 20b.

[0091] As illustrated in Figures 1 1A, 1 1B, a layer 231 made of an electrically insulating material, for example a layer of alumina (A12O3) with a thickness of between 20 nm and 100 nm, is deposited on the surface of the second sacrificial layer 20b and on the upper face 221 of the support pillars 22. Photolithography and etching steps make it possible to remove the layer 231 of A12O3 deposited on the upper face of the second sacrificial layer 20b. A portion of the layer 231 located at the edge of the upper face 221 of the support pillar 22, on the upper face of the second sacrificial layer 20b, can be retained. This portion can typically extend over 250 nm to 500 nm. This insulating layer 231 has the function of electrically insulating the support pillar 22, which is here electrically connected to the anchoring pillar 21 and to the detectors, from the encapsulation layer 23 of amorphous silicon, itself conductive.

[0092] The encapsulation layer 23 made of amorphous silicon is then deposited on the layer 231 and on the surface of the second sacrificial layer 22b. The encapsulation layer 23 may have a uniform thickness of between 200 nm and 800 nm. The encapsulation layer 23 is here essentially planar.

[0093] The rest of the method is identical to the previous embodiment, and includes the formation of the vents 230, the removal of the sacrificial layers 20a, 20b by chemical attack in HF vapor, the deposition of the sealing and antireflection layers 24, 25, as illustrated in FIGS. 12A, 12B.

[0094] In the following, different variants on the principle of a support pillar comprising a lower portion in contact with at least one flank of the anchor pillar are described and illustrated.

[0095] Figures 13A, 13B, 13C illustrate in top view certain variants of formation of the first opening 300, which conditions the morphology of the second opening 200 and ultimately the morphology of the lower portion of the support pillar. [Fig. 13A] illustrates the case already described with reference to Figures 5A, 5B, where the first opening 300 is located, in projection in the xy plane, astride the underlying anchoring pillar 21, on the overhang 31 and extends laterally along y above the first sacrificial layer. The first opening 300 extends here on either side of the overhang 31 and breaks the continuity of the overhang 31. [Fig. 13B] illustrates the case in which the first opening comprises two opening parts 300a, 300b located on two overhangs 31a, 31b. This doubles the contact area between the support pillar and the anchor pillar, compared to the case illustrated in [Fig. 13A].The adhesion and mechanical strength of the support pillar on the anchor pillar are improved. The first opening portion 300a extends transversely to the first overhang 31a, similarly to the case illustrated in [Fig. 13A]. The first overhang 31a is located on a first side of the intermediate structure 3. The second opening portion 300b extends transversely to the second overhang 31b. The second overhang 31b is located on a second side of the intermediate structure 3, preferably opposite the first side. This makes it possible to balance the distribution of tensile forces on the intermediate structure. intermediate. [Fig.l3C] illustrates the case in which the first opening comprises two opening portions 300a, 300b internal to the overhangs 31a, 31b. In this case, the opening portions 300a, 300b do not extend along y beyond the overhangs 31a, 31b. The continuity of each overhang 31a, 31b is preserved. The rigidity of the intermediate structure is optimized. This type of opening nevertheless requires a better photolithography resolution than the cases illustrated in FIGS. 13A, 13B. [Fig.l3D] illustrates the superposition of a second opening pattern 200 on the first opening portions 300a, 300b. According to a preferred possibility, this second opening pattern 200 extends laterally beyond the flanks 210 of the anchoring pillar 21, but remains confined within the perimeter of the overhangs 31a, 31b of the intermediate structure. The lateral bulk of the support pillar thus remains limited.

[0096] The electrical contact zone 410 (where the TiN of the layer 302 is in contact with the TiN of the wafer 310, see for example FIGS. 4A, 4B in section) can: - either be inscribed in the imprint of the anchor pillar delimited by the flank 210 (this is the case shown in the figures), - or extend beyond the anchoring pillar delimited by the flank 210 while remaining inscribed in the imprint of the wafer 310 (case not shown in the figures).

[0097] Figures 14A, 14B illustrate in sections an embodiment comprising only the formation of the second opening, without prior formation of a first opening. In this embodiment, the intermediate structure is not etched. The second opening passes around the overhang 31 during the anisotropic etching, then under the overhang 31 during the isotropic etching, to arrive in contact with the flank 210 of the anchoring pillar. To facilitate the extension of the second opening under the overhang 31, the width of the overhang 31 along y is reduced during the formation of the intermediate structure. In this embodiment, the overhang 31 forms an overhang with respect to the flank 210 of the anchoring pillar 21, over a lateral distance preferably between 0.2 pm and 0.3 pm.To form the second opening 200, an opening pattern comprising a first lateral extension 200a and / or a second lateral extension 200b, as illustrated in [Fig. 15], is typically used. These lateral extensions 200a and / or 200b extend beyond the perimeter of the one or more overhangs 31a, 31b, directly above the first sacrificial layer.

[0098] An anisotropic etching step along z makes it possible to etch the second sacrificial layer over its entire thickness, selectively to the materials of the intermediate structure, and to etch in the extension only a part of the thickness of the first sacrificial layer, typically over a depth of between 200 nm and 800 nm.

[0099] At the end of the anisotropic etching by RIE, the etched portion of the first sacrificial layer is aligned vertically with the outer perimeter of the overhang of the structure in intermediate. This etched portion is therefore separated from the flank of the anchor pillar by a distance of approximately 0.2 pm to 0.3 pm, corresponding to the overhang formed by the overhang with the flank of the anchor pillar. An isotropic etching, typically by wet etching, is provided here in such a way that the second opening extends under the lower face of the overhang over a distance at least equal to the distance separating the anisotropic etching front from the flank of the anchor pillar. This can be achieved by adjusting the wet etching time. It is advantageous to provide an additional etching time so as to clear a larger surface area of ​​the flank of the anchor pillar. This makes it possible to form a more extensive direct contact between the support pillar and the anchor pillar.

[0100] This embodiment saves at least one method step dedicated to forming the first opening. However, the support pillar is not in contact with the upper face of the anchor pillar in this embodiment. In this example, the portion 220 of the support pillar 22 comprises a first part 220a passing around the overhang 31, and a second part 220b under the overhang 31. Only the second part 220b is in contact with the flank 210 of the anchor pillar 21. The first part 220a has a first dimension La along y, and the second part 220b has a second dimension Lb along y strictly greater than the first dimension La. This makes it possible to form a stop for the portion 220 against the overhang 31. The mechanical tensile strength of the support pillar 22 on the anchor pillar 21 is improved.

[0101] In view of the foregoing description, it is clear that the proposed device and method offer a particularly effective solution for improving the adhesion of the support pillars of the encapsulation structure by direct contact with the anchoring pillars. This contact between solid pillars makes it possible to significantly improve the mechanical strength of the encapsulation structure. The support pillars can also advantageously come into abutment against a lower face of the overhang of the intermediate structure, to improve the tensile strength of the encapsulation structure.

[0102] The invention is not limited to the embodiments previously described.

[0103] For a plurality of support pillars on corresponding anchor pillars, each support pillar preferably comprises a lower portion in contact with the underlying anchor pillar. Other options are possible where only a subset of the support pillars comprises a lower portion in contact with the underlying anchor pillar, for example every other support pillar, for example arranged in a staggered pattern or any other arrangement that a person skilled in the art will be able to define in view of the present description. The cavity formed within the encapsulation structure may typically house a so-called "getter" material intended to trap residual gases in the cavity, to improve the reliability and lifetime of the detection device. The support pillars and / or anchor pillars may include other layers, for example a barrier layer to the diffusion of metal atoms in TiN.

Claims

Claims

1. Device (1) for detecting electromagnetic radiation, comprising at least one detector arranged within a cavity (2) formed by an encapsulation structure, said encapsulation structure comprising anchoring pillars (21) of which at least one is connected to the at least one detector, and support pillars (22) surmounting said anchoring pillars (21), the device (1) being characterized in that the support pillars (22) have a portion (220) extending over at least one flank (210) of the anchoring pillars (21).

2. Device (1) according to the preceding claim comprising an intermediate structure (3) between the support pillars (22) and the anchoring pillars (21), said intermediate structure (3) having: • an isolation arm (30) configured to support the at least one detector, and • at least one overhang (31) around an upper face (211) of the anchoring pillars (21), in which the portion (220) of the support pillars (22) passes around the at least one overhang (31) or through the at least one overhang (31).

3. Device (1) according to the preceding claim in which the portion (220) of the support pillars (22) comprises a first part (220a) at the level of the at least one overhang (31) having a first dimension La in a reference direction (x, y), and a second part (220b) beyond the at least one overhang (31) on the at least one flank (210) of the anchoring pillars (21) and having a second dimension Lb in the reference direction (x, y), such that the second dimension Lb is strictly greater than the first dimension La.

4. Device (1) according to the preceding claim in which at least the second part (220b) of the portion (220) of the support pillars (22) is in contact with at least one flank (210) of the anchoring pillars (21).

5. Device (1) according to the preceding claim in which the first and second parts (220a, 220b) of the portion (220) of the support pillars (22) are in contact with at least one flank (210) of the anchoring pillars (21).

6. Device (1) according to any one of the three claims- preceding indications in which the first part (220a) of the portion (220) of the support pillars (22) is in contact with the upper face (211) of the anchor pillars (21).

7. Device (1) according to any one of the preceding claims in which the portion (220) of the support pillars (22) extends over a first flank (210a) of the anchoring pillars (21), located on a first side, and extends over a second flank (210b) of the anchoring pillars (21), located on a second side opposite the first side.

8. Device (1) according to any one of the preceding claims wherein the cavity (2) is closed by an encapsulation layer (23) of an encapsulation material bearing on the support pillars (22), and by a sealing layer (24) of a sealing material on said encapsulation layer (23), and wherein the support pillars (22) are at least partly formed by the encapsulation layer (23) alone or by the encapsulation layer (23) and the sealing layer (24), so that the support pillars (22) comprise the encapsulation material alone or the encapsulation material and the sealing material.

9. A method of manufacturing a device (1) for detecting electromagnetic radiation according to any one of the preceding claims comprising: • Providing a substrate (100), • Forming a first sacrificial layer (20a) on said substrate (100), • Forming the anchoring pillars (21) through said first sacrificial layer (20a), • Arranging at least one detector above the first sacrificial layer (20a) and forming a connection between the at least one detector and at least one anchoring pillar (21) among the anchoring pillars (21), • Forming a second sacrificial layer (20b) on the first sacrificial layer (20a), on the at least one detector and on the anchoring pillars (21), • Forming a second opening (200) in said second sacrificial layer (20b) above the anchoring pillars (21), said second opening (200) extending over at least one flank (210) of the anchor pillars (21),and extending from, preference in the first sacrificial layer (20a), • Filling said second opening (200) with at least one filling material so as to form the support pillars (22) surmounting the anchor pillars (21), • Forming an encapsulation layer (23) of an encapsulation material on the second sacrificial layer (20b) and at least partly on the support pillars (22), • Form at least one vent (230) within the encapsulation layer (23), said vent (230) opening onto the second sacrificial layer (20b), • Removing the second and first sacrificial layers (20b, 20a) through the at least one vent (230), so as to form a cavity (2) around the at least one detector, • Forming a sealing layer (24) of a sealing material on the encapsulation layer (23) so as to seal the at least one vent (230).

10. Method according to the preceding claim further comprising, after formation of the first sacrificial layer (20a) and before formation of the second sacrificial layer (20b), formation of an intermediate structure (3) between the support pillars (22) and the anchoring pillars (21), said intermediate structure (3) having: • an isolation arm (30) configured to support the at least one detector, said isolation arm (30) forming the connection between said at least one detector and the at least one anchoring pillar (21) among the anchoring pillars (21), • at least one overhang (31, 31a, 31b) around an upper face (211) of the anchoring pillars (21), wherein forming the second opening (200) comprises • An anisotropic etching configured to extend the second opening (200) under and in line with the at least one overhang (31, 31a, 31b), • An isotropic etching configured to extend the second opening (200) under the at least one overhang (31) and against the at least one flank (210) of the anchor pillars (21), so that, after filling said second opening (200), the portion (220) of the support pillars (22) has a first part (220a) at the level of the at least one overhang (31) having a first dimension La in a reference direction (x, y), and a second part (220b) below the at least one overhang (31) on the at least one flank (210) of the anchoring pillars (21) and having a second dimension Lb in the reference direction (x, y), such that the second dimension Lb is strictly greater than the first dimension La.

11. A method according to any one of claims 9 to 10 further comprising, after formation of the intermediate structure (3), a formation of a first opening (300) in the intermediate structure (3), said first opening (300) partially exposing the upper face (211) of the anchoring pillars (21) and passing through the at least one overhang (31) around the perimeter of the anchoring pillars (21), and wherein the formation of the second opening (200) in the second sacrificial layer (20b) is configured so that said second opening (200) passes at least partially through the first opening (300).

12. A method according to any one of claims 9 to 11 wherein the filling of the second opening (200) is at least partially carried out during the formation of the encapsulation layer (23), by conformal deposition of said encapsulation layer (23) on the second sacrificial layer (20b) and in the second opening (200), so that the at least one filling material comprises the encapsulation material.

13. Method according to the preceding claim in which the filling of the second opening (200) is at least partially carried out during the formation of the sealing layer (24), by depositing said sealing layer (24) on the encapsulation layer (23), so that the at least one filling material comprises the encapsulation material and the sealing material.

14. Method according to any one of claims 9 to 11 in which the filling of the second opening (200) is carried out before the formation of the encapsulation layer (23), by a replacement material different pleating of the encapsulating material.

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