Method of manufacturing a detection device with improved getter protection

Abstract

The invention relates to a method for manufacturing a detection device comprising the steps of: • producing a getter pad (50) based on amorphous carbon located on a mineral sacrificial layer (62) covering a thermal detector (20); • producing a thin encapsulation layer located on the mineral sacrificial layer (62) and covering the upper surface and the lateral walls of the getter pad (50); • removing the mineral sacrificial layer by a first chemical etching; • removing the protective segment (51) of the getter pad (50) by a second chemical etching.

Description

Technical Field

[0001] The field of the invention is that of devices for detecting electromagnetic radiation, in particular infrared or terahertz radiation, comprising at least one thermal detector enclosed in a sealed cavity in which a getter material is also located. The invention is particularly applicable to the fields of infrared imaging and thermal imaging. Background Art

[0002] The device for detecting electromagnetic radiation, such as infrared or terahertz radiation, may comprise a matrix of thermal detectors, each thermal detector comprising an absorbing segment capable of absorbing the electromagnetic radiation to be detected.

[0003] To ensure thermal insulation of the thermal detector, the absorbing section typically takes the form of a membrane suspended above the substrate by anchoring posts and thermally insulated from the substrate by retaining and insulating arms. These anchoring posts and support arms also perform an electrical function by electrically connecting the suspended membrane to readout circuitry, which is typically located in the substrate.

[0004] The readout circuitry typically takes the form of a CMOS circuit. It allows a control signal to be applied to the thermal detector and a detection signal generated by the thermal detector in response to the absorption of the electromagnetic radiation to be detected to be read. The readout circuitry comprises various electrical interconnect layers formed by metal lines separated from one another by dielectric layers (called intermetallic layers). At least one electrical connection pad of the readout circuitry is placed on the substrate so that it can be contacted from outside the detection device.

[0005] Document EP3239670A1 describes a method for manufacturing a detection device in which a thermal detector is arranged in a sealed cavity. The method uses a mineral sacrificial layer to produce the thermal detector and the packaging structure that defines the cavity, and these layers are subsequently removed by wet chemical etching. The cavity is defined by a thin packaging layer that extends above and around one or more thermal detectors. The cavity is created by depositing an upper mineral sacrificial layer on the upper surface and in grooves extending through the mineral sacrificial layer. Therefore, the thin packaging layer is formed by an upper wall located on the upper mineral sacrificial layer and a peripheral wall located on the substrate and surrounding one or more thermal detectors in a plane parallel to the substrate. This configuration significantly allows the footprint of the packaging structure on the substrate to be reduced.

[0006] Furthermore, the manufacturing method described in this document provides for the formation of a segment of getter material, for example titanium, in a sealed cavity. This getter segment is then located beneath each absorber membrane and protected from wet chemical etching by a thin sacrificial carbon layer, for example made of amorphous carbon, which is subsequently removed by a specific dry chemical etch.

[0007] However, while keeping the footprint of the package structure on the substrate small, there is a need to enhance the protection of the getter material during the removal of the mineral sacrificial layer by wet chemical etching. Summary of the Invention

[0008] The object of the present invention is to at least partially remedy the disadvantages of the prior art. To this end, a subject of the present invention is a method for manufacturing a device for detecting electromagnetic radiation, comprising the following steps:

[0009] producing at least one thermal detector for detecting electromagnetic radiation, said at least one thermal detector being located on a substrate and covered by a mineral sacrificial layer made of a mineral material, said mineral sacrificial layer being removable by a first chemical etch;

[0010] Producing at least one pad, called a getter pad, which:

[0011] o extending partially over the mineral sacrificial layer and disposed remote from the thermal detector in a plane parallel to the substrate,

[0012] o formed by a stack of segments of thin planar layers parallel to one another, comprising a protection segment made of amorphous carbon and at least one getter segment made of a getter material, said protection segment being removable by a second chemical etch and being in contact with the mineral sacrificial layer, said at least one getter segment being in contact with the protection segment;

[0013] creating a thin encapsulation layer extending over the thermal detector, the thin encapsulation layer comprising an upper portion located on the mineral sacrificial layer and covering the upper surface and sidewalls of the getter pad;

[0014] creating at least one first vent through the thin encapsulation layer, said at least one first vent being located away from the getter pad in a plane parallel to the substrate and opening into the mineral sacrificial layer;

[0015] Removal of the mineral sacrificial layer by a first chemical etch, thereby releasing the surface of the protective segment;

[0016] Removing the protective segment by a second chemical etch, thereby releasing the surface of the getter segment;

[0017] • Depositing a thin sealing layer over the thin encapsulation layer so as to block at least the first vent.

[0018] By removing the mineral sacrificial layer by means of a first chemical etch, it is meant that this layer is at least partially removed in order to release the surface of the protective segment.

[0019] The following are certain preferred but non-limiting aspects of the manufacturing method.

[0020] The manufacturing method may comprise the step of manufacturing at least one compensation detector which does not receive the electromagnetic radiation to be detected, the getter pad being arranged facing the compensation detector.

[0021] A plurality of thermal detectors and compensation detectors may be produced, with at least one getter pad being arranged facing the compensation detector.

[0022] Each of the thermal detector and the compensation detector may include a membrane suspended above a substrate by anchoring posts, the thin encapsulation layer including at least one support post integrally formed with the upper portion and extending from the upper portion to rest on the anchoring posts.

[0023] The manufacturing method may comprise a step of producing a layer made of electrically insulating material, said layer being placed between and in contact with the support and anchoring posts.

[0024] After the step of producing a thin encapsulation layer, the thin encapsulation layer can extend continuously above and around the thermal detector and be formed by an integrally formed upper portion and a surrounding portion, the surrounding portion of the thin encapsulation layer extending into the trench produced through the mineral sacrificial layer and contacting its sidewalls, and the surrounding portion is located on the substrate.

[0025] The getter pad may include a plurality of getter segments stacked along an axis perpendicular to the substrate, each of the plurality of getter segments being disposed between two protection segments.

[0026] The getter segment may completely cover the face of the protective segment opposite to the substrate.

[0027] During the step of producing the first vent, at least one second vent can be produced through the thin encapsulation layer to give access to the upper protective segment covering the getter segment, and then, after the step of removing the mineral sacrificial layer, a hole can be produced from the second vent to give access to the lower protective segment on which the getter segment is located.

[0028] A second thin sealing layer may be deposited to block the second vent, the second thin sealing layer being different from the thin sealing layer blocking the first vent.

[0029] The getter pad may include a plurality of getter segments and a plurality of protection segments, wherein the plurality of getter segments and the plurality of protection segments are stacked along an axis perpendicular to the substrate. The lateral overetching of the protection segments may be performed selectively relative to the getter segments.

[0030] The mineral sacrificial layer may be made of silicon oxide obtained from tetraethyl orthosilicate.

[0031] Furthermore, during the generation of the at least one thermal detector, the at least one thermal detector may be located on a first sacrificial mineral layer, the thermal detector and the first sacrificial mineral layer being covered by a second sacrificial mineral layer, the first and second sacrificial mineral layers being made of a mineral material that can be removed by a first chemical etch. A first vent may be positioned facing the thermal detector, or, where appropriate, facing the matrix of thermal detectors. During the first chemical etch, which may be a wet etch in an acidic medium, the first and second sacrificial mineral layers may be partially removed through the first vent, with the unetched sections of the first and second sacrificial mineral layers forming a peripheral wall surrounding the thermal detector (or, where appropriate, the matrix of thermal detectors) in a plane parallel to the substrate. The upper portion of the encapsulation layer is positioned on and in contact with the peripheral wall.

[0032] After the first chemical etching, the peripheral wall may comprise a transverse groove which causes the cavity to widen vertically parallel to the read-out substrate between the read-out substrate and the upper part, the transverse groove defining an intermediate area of ​​the surface of the read-out substrate which surrounds the thermal detector or, where appropriate, a matrix of thermal detectors.

[0033] The method may include a step of producing reinforcement pillars for reinforcing the thin encapsulation layer, the reinforcement pillars being arranged in an intermediate region around the thermal detectors or, where appropriate, separately from one another in a matrix of thermal detectors and extending from above to lie on the readout substrate. The reinforcement pillars may lie directly on the substrate, and thus in contact with it, or indirectly on the substrate, for example in contact with anchoring pillars. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Other aspects, objects, advantages and features of the present invention will become more apparent from the following detailed description of preferred embodiments thereof, which is given by way of non-limiting example and with reference to the accompanying drawings, in which:

[0035] Figures 1A to 1I are schematic and partial cross-sectional views of various steps of a method for manufacturing a detection device according to a first embodiment;

[0036] Figures 2A to 2D are schematic and partial cross-sectional views of various steps of a method for manufacturing a detection device according to a variant embodiment, in which lateral overetching is performed on certain parts of the layer forming the getter pad;

[0037] Figure 3 is a top view of a detection device according to one embodiment, showing an arrangement of a thermal detector and a compensation detector, and a getter segment;

[0038] Figures 4A to 4Care schematic and partially cross-sectional views of various steps of a method for manufacturing a detection device according to another variant embodiment, wherein a specific sealing layer covers a getter pad;

[0039] Figures 5A to 5C are schematic and partial cross-sectional views of various steps of a method for manufacturing a detection device according to another variant embodiment;

[0040] Figures 6A to 6C are schematic and partially cross-sectional views of various steps of a method for manufacturing a detection device according to another variant embodiment, wherein the encapsulation structure comprises a peripheral wall made of a mineral material;

[0041] 7A to 7C are schematic and partially cross-sectional views of various steps of a method for manufacturing a detection device according to another variant embodiment, wherein the encapsulation structure comprises a peripheral wall made of a mineral material and wherein the mineral sacrificial material is removed through the first and second ventilation openings. DETAILED DESCRIPTION

[0042] In the drawings and the remainder of the specification, the same reference numerals are used to represent the same or similar elements. In addition, for the sake of clarity of the drawings, various elements are not shown to scale. In addition, the various embodiments and variations are not mutually exclusive and can be combined with each other. Unless otherwise specified, the terms "substantially," "approximately," and "the order of magnitude of..." mean within 10%, preferably within 5%. In addition, unless otherwise specified, the terms "included between..." and "and equivalents are meant to include limits.

[0043] The present invention generally relates to a method for manufacturing a device for detecting electromagnetic radiation, which device is suitable for detecting infrared or terahertz radiation. The detection device comprises one or more thermal detectors and at least one material having a getter effect located in a sealed cavity. The sealed cavity is delimited by a packaging structure, which comprises a plurality of thin layers, which are transparent to the electromagnetic radiation to be detected and in particular comprises a thin packaging layer that extends continuously above one or more thermal detectors and optionally extends continuously above and around the thermal detectors. A thin layer is a layer formed using material deposition techniques used in microelectronics and preferably has a thickness of less than or equal to 10 μm. In addition, a thin layer is said to be transparent when its transmittance at the central wavelength of the spectral range of the electromagnetic radiation to be detected is higher than or equal to 50%, preferably higher than or equal to 75%, or even higher than or equal to 90%.

[0044] In general, a material with a getter effect is one that is intended to be exposed to the atmosphere of a sealed cavity and capable of pumping gases by absorption and / or adsorption. It is a metal that can be chosen from titanium, zirconium, vanadium, chromium, cobalt, iron, manganese, palladium, barium and / or aluminum, or even an alloy of these metals, such as TiZrV.

[0045] The manufacturing method also includes a step of forming one or more thermal detectors by means of at least one sacrificial layer, called a mineral sacrificial layer, made of a mineral or inorganic material. Silicon-based dielectric materials can also be used to form the intermetallic dielectric layer of the readout circuit, i.e., electrically insulating materials having a dielectric constant or relative permittivity, for example, lower than or equal to 3.9, thereby limiting the parasitic capacitance between interconnects. Such mineral materials have no carbon chains and can be silicon oxide SiO x or silicon nitride Si x N y , or organosilicon materials (e.g., SiOC, SiOCH), or fluoride glass-type materials (e.g., SiOF). The mineral sacrificial layer can be removed by wet chemical etching, such as chemical etching in an acidic medium, such as gaseous hydrofluoric acid (HF vapor). Wet etching generally refers to the etchant being in the liquid phase or gas phase, preferably the gas phase.

[0046] Furthermore, the getter segments are protected by protective segments made of amorphous carbon, provided that one or more mineral sacrificial layers are removed after the thin encapsulation layer has been created. The amorphous carbon may optionally be of the DLC type (Diamond like Carbon), i.e. a carbon that exhibits a high sp 3 The protective segment is essentially inert with respect to the wet chemical etching performed to remove the mineral sacrificial layer. Essentially inert means that the amorphous carbon does not react substantially, or even reacts very little, with the etchant used in the step of removing the mineral sacrificial layer, so that at the end of this removal step, the protective segment still protects the getter material. The thin protective layer is suitable for removal by chemical etching (e.g., dry chemical etching) using, for example, oxygen contained in a plasma as an etchant.

[0047] Figures 1A to 1I The various steps of a method for manufacturing a detection device 1 according to one embodiment are shown. For clarity, only a portion of the detection device 1 is shown in the figure. In this example, the thin encapsulation layer extends continuously over and around the thermal detector. However, other configurations of the thin encapsulation layer are also possible.

[0048] By way of example, the thermal detector 20 is suitable here for detecting infrared radiation in the LWIR (Long Wavelength Infrared) range, whose wavelength is approximately 8 μm to 14 μm. Each detection device 1 comprises one or more thermal detectors 20, and here a matrix of identical thermal detectors, which are connected to a readout circuit located in a substrate 10 (hence the readout substrate) and are located in the same sealed cavity 2. The thermal detectors 20 thus form periodically arranged sensitive pixels, and they may have lateral dimensions in the plane of the readout substrate 10 of the order of tens of micrometers, for example equal to approximately 10 μm or less. As a variant, the detection device 1 may comprise a plurality of sealed cavities 2, each of said plurality of sealed cavities containing a single thermal detector 20.

[0049] Here, a three-dimensional direct coordinate system XYZ is defined, wherein the XY plane is substantially parallel to the plane of the readout substrate 10, and the Z axis is oriented toward the thermal detector 20 in a direction substantially perpendicular to the plane of the readout substrate 10. The terms "vertical" and "vertically" should be understood to relate to a direction substantially parallel to the Z axis, and the terms "horizontal" and "horizontally" should be understood to relate to a direction substantially parallel to the plane (X, Y). In addition, the terms "lower" and "upper" will be understood to relate to positions with increasing distance from the readout substrate 10 in the +Z direction.

[0050] Reference Figure 1A , at least one thermal detector 20, here a plurality of thermal detectors 20, is produced on a readout substrate 10, these thermal detectors 20 being covered by at least one mineral sacrificial layer 62. In this example, a plurality of compensation detectors 3 are also produced.

[0051] The readout substrate 10 is silicon-based and is formed by a carrier substrate 11 containing a readout circuit (not shown) suitable for controlling and reading the thermal detector 20. The readout circuit here takes the form of a CMOS integrated circuit. It comprises, in particular, conductor segments separated from one another by metal-to-metal insulating layers made of a dielectric material, for example a silicon-based mineral material, such as silicon oxide (SiO x ), silicon nitride (SiN x ) etc. The conductive segments 12 are flush with the surface of the carrier substrate 11 and ensure electrical connection between the anchoring posts 21 of the thermal detector 20 and the readout circuit. In addition, one or more connecting segments (not shown) are flush with the surface of the carrier substrate and allow the readout circuit to be connected to external electronic devices.

[0052] The readout substrate 10 may include a reflector 13 positioned facing each thermal detector 20. The reflector 13 may be formed by a wire segment of the last interconnect level, the wire being made of a material suitable for reflecting the electromagnetic radiation to be detected. It faces the absorption film 23 of the thermal detector 20 and is intended to form a quarter-wavelength interference cavity with the absorption film for the electromagnetic radiation to be detected.

[0053] Finally, the readout substrate 10 here comprises a protective layer 14, so as to substantially cover the upper intermetallic insulating layer. This protective layer 14 corresponds here to an etch stop layer made of a material that is substantially inert to the chemical etchants subsequently used to remove the various mineral sacrificial layers 61, 62, for example in a gaseous HF medium. This protective layer 14 thus forms an electrically insulating, chemically inert sealing layer to prevent any short circuits between the anchor posts 21. Thus, the underlying intermetallic insulating layer is prevented from being etched during the step of removing the mineral sacrificial layer. It can be formed of aluminum oxide or aluminum nitride, or even of aluminum trifluoride, or even of unintentionally doped amorphous silicon.

[0054] Thermal detectors 20 are then produced on the readout substrate 10. These production steps are clearly identical or similar to those described in document EP3239670A1. The thermal detectors 20 are microbolometers, each of which includes an absorber film 23, i.e., a film capable of absorbing the electromagnetic radiation to be detected, suspended above the readout substrate 10 by anchoring posts 21 and thermally insulated from the substrate by retaining and thermally insulating arms (not shown). The absorber film 23 is typically obtained using surface micromachining techniques that include producing the anchoring posts 21 through a first sacrificial mineral layer 61, and producing the thermally insulating arms and absorber film 23 on the upper surface of the sacrificial mineral layer 61. Each absorber film 23 also includes a temperature sensor, such as a thermistor material, connected to the readout circuitry via electrical connections provided in the thermally insulating arms and anchoring posts 21. In this example, the detection device 1 includes an optically active thermal detector 20, i.e., a detector intended to detect the electromagnetic radiation of interest. It also includes one or more detectors, referred to as compensation detectors 3, i.e., detectors not intended to receive the electromagnetic radiation of interest. The compensation detector 3 is intended to measure a common-mode electrical signal which will be subtracted from the electrical signal measured by the optically active thermal detector 20 .

[0055] Next, a second mineral sacrificial layer 62 is deposited, preferably having the same properties as the first mineral sacrificial layer 61. The second mineral sacrificial layer 62 covers the mineral sacrificial layer 61, the thermal detector 20, and the compensation detector 3. It has a substantially flat upper surface along the Z axis opposite the readout substrate 10. Typically, the various mineral sacrificial layers 61, 62 can be silicon oxide obtained using a tetraethylorthosilicate (TEOS) compound and deposited by PECVD.

[0056] Reference Figure 1B , a stack 40, called a getter stack, is then deposited, which is used to produce one or more pads 50, called getter pads, which will be described in detail below. This stack 40 is called a getter stack if it comprises at least one thin getter layer 42 and at least one thin protective layer 41 made of amorphous carbon. It is produced so as to cover the upper surface of the mineral sacrificial layer 62 and, here, faces the optically active thermal detector 20 and the compensation detector 3. The getter stack 40 is formed by a stack of a plurality of thin planar layers 41, 42, parallel to each other along the Z axis, comprising at least a lower protective layer 41.1 situated on and in contact with the mineral sacrificial layer 62, and a getter layer 42.1 situated on and in contact with the lower protective layer 41.1. The thin layers 41, 42 of the getter stack 40 are considered planar if they extend in a planar manner over their entire area in the XY plane.

[0057] In this example, the getter stack 40 comprises a plurality of getter layers 42.1, 42.2, here two layers, each getter layer 42 being located between and in contact with two protective layers 41. The number of getter layers 42 is selected according to the desired effective surface area of ​​the getter material in the sealed cavity 2. The fact that the protective layer 41.3 covers the upper getter layer 42.2 is useful when a vent 33 is present through the thin encapsulation layer 31 and leads to the getter pad 50 (see FIG. Figure 1E ). The underlying getter segment 52.2 is then protected from the wet etchant used during the step of removing the mineral sacrificial layers 61, 62. The protective layer 41 is made of amorphous carbon and can have a thickness of 50 nm to 500 nm. The getter layer 42 can be made of titanium, for example, and can have a thickness of approximately 100 nm to 1 μm, typically 300 nm.

[0058] Reference Figure 1C , a plurality of pads 50, called getter pads, are produced by photolithography and local etching of the getter stack 40. Etching is performed so as to locally etch the getter stack 40 up to its thickness, thereby leading to the mineral sacrificial layer 62. When the plurality of getter pads 50 are produced, they are separated and away from each other in the XY plane. Thus, one or more getter pads 50 partially cover the mineral sacrificial layer 62. Furthermore, they are formed by a stack of segments 51, 52 of said thin planar layers 41, 42, and therefore each comprises a lower protective segment 51.1 made of amorphous carbon situated on and in contact with the mineral sacrificial layer 62, and a getter segment 52.1 situated on and in contact with the lower protective segment 51.1.

[0059] The getter pads 50 are positioned in the XY plane away from the optically active thermal detectors 20 so as not to interfere with the transmission of the electromagnetic radiation to be detected. They are therefore located in the XY plane at a non-zero distance from the absorbing films 23 of these thermal detectors 20, and advantageously at a non-zero distance from the thermally insulating arms and their anchoring posts 21. In this example, they are positioned facing the compensation detector 3, i.e., vertically along the Z axis, in order to shield the incident electromagnetic radiation.

[0060] In this figure, a single compensation detector 3 and a single getter pad 50 are shown, although there may be multiple compensation detectors 3 and multiple getter pads 50. One or more getter pads 50 may have a size of about a few microns to tens of microns in the XY plane, preferably less than or equal to 50 μm, to ensure good mechanical retention. One or more getter pads 50 may have a variable number and arrangement in the XY plane. Thus, for example, the same getter pad 50 may extend towards multiple compensation detectors 3. In this case, holes (not shown here) may be locally made in the getter pad 50 to allow the manufacture of support columns for supporting the thin encapsulation layer 31. It may include multiple holes (as described below) to allow access to the intermediate protection section 51 where appropriate. As a variant, multiple getter pads 50 may be produced, which are arranged so that there is one getter pad 50 for each compensation detector 3. Other arrangements are of course possible.

[0061] Advantageously, one or more grooves 63 are then made to allow for the formation of support posts 31.3. These grooves are particularly useful when the sealed cavity 2 includes a large number of thermal detectors 20. These grooves 63 extend from the upper surface of the mineral sacrificial layer 62 along the Z axis to provide access to at least a portion of the anchor posts 21 of the thermal detectors 20 and / or compensation detectors 3. A thin insulating layer 64 made of an electrically insulating material is then deposited on the released surface of the anchor posts 21 within the grooves 63. This thin insulating layer 64 prevents electrical short circuits between the detectors 3 and 20 through the thin encapsulation layer 31 and its support posts 31.3. The thin insulating layer 64 is preferably etched locally toward the thermal detectors 20 so as not to reduce the transmission of the electromagnetic radiation to be detected. Its thickness can be approximately 10 nm to 100 nm. It is made of a material that is inert to the wet chemical etching used to remove the mineral sacrificial layers 61, 62, and this material can be selected from AlN, Al2O3, and HfO2.

[0062] Reference Figure 1DThen, for each matrix of thermal detectors 20, the thin encapsulation layer 31 of the encapsulation structure 30 is produced in a manner similar to that described in document EP 3 239 670 A1. First, using conventional photolithographic techniques, the mineral sacrificial layers 61, 62 are locally etched to form trenches leading to the readout substrate 10. The trenches (or continuous trenches) together form a continuous and closed perimeter surrounding the thermal detectors 20 and the compensation detector 3 in the XY plane.

[0063] Next, a thin encapsulation layer 31 is conformally deposited, for example by chemical vapor deposition (CVD). Here, the thin encapsulation layer is made of amorphous silicon with a thickness of approximately 800 nm (although other materials, such as Ge or SiGe, may also be used). This thin encapsulation layer extends over the mineral sacrificial layer 62 and into the trench, in this case, the groove 63. Thus, the thin encapsulation layer 31 includes an upper portion 31.1 (also referred to as the upper wall), which extends a distance above the thermal detector 20 along the Z axis and covers the mineral sacrificial layer 62 and the getter pad 50. It also includes a peripheral portion 31.2 (also referred to as the peripheral wall), which continuously surrounds the thermal detector 20 in the XY plane and contacts the sidewalls of the mineral sacrificial layers 61 and 62. Here, it also includes a support post 31.3 extending along the Z axis from the upper wall 31.1 to the anchor post 21. The upper wall 31.1, the peripheral wall 31.2, and the support post 31.3 are formed integrally. Thus, the upper wall 31.1 of the thin encapsulation layer 31 extends over the upper surface of the mineral sacrificial layer 62, over the sidewalls and over the upper surface of the one or more getter pads 50. A sidewall is a surface of a layer or layer segment which extends along an axis substantially perpendicular to the substrate and defines the boundaries of the layer or layer segment in the XY plane.

[0064] Reference Figure 1E First vents 32 are created through the thin encapsulation layer 31 to provide access to the mineral sacrificial layer 62 and are intended to allow the various mineral sacrificial layers 61, 62 to be removed from the cavity 2. They are positioned away from the getter pad 50. In this example, the vents 32 are positioned perpendicular to the absorber film 23 of the thermal detector 20, but they could be located elsewhere. Preferably, at the same time, second vents 33 are created through the thin encapsulation layer 31 and the thin insulating layer, here leading to the upper protective section 51.3 of the getter pad 50.

[0065] Reference Figure 1F, perform the first chemical etching suitable for removing the mineral sacrificial layers 61, 62, here is a wet chemical etching by gas phase hydrofluoric acid etching. The product of the chemical reaction is discharged through the first vent 32. Because this wet chemical etching is isotropic, the suspension of the absorption film 23 is achieved, and the anchor column 21, the thermal insulation arm and the support column 31.3 are released. The first chemical etching is selective so that the lower protection section 51.1 of the getter pad 50 is not removed, and the getter section 52 is therefore completely protected from HF vapor etching. Therefore, the lower surface of the protection section 51.1 is released, that is, its surface that was originally in contact with the mineral sacrificial layer 62 is now released. Therefore, the upper wall 31.1 of the thin encapsulation layer 31 is located on the readout substrate 10 through the peripheral wall 31.2 and here through the support column 31.3, and the support column rests on the anchor column 21.

[0066] Reference Figure 1G , the depth of the second vent 33 is extended to form at least one hole 53, which is self-aligned on the second vent 33 and extends through the getter pad 50 in the direction of the readout substrate 10, so as to allow the etchant of the second chemical etching to reach all the protection segments 51, here in particular the middle protection segment 51.2. In this example, the hole 53 is a through hole, as long as it passes through each protection segment 51 and each getter segment 52. However, it may not be a through hole and only partially extend through the lower protection segment 51.1 (see Figure 4A This step can be performed using a conventional dry etchant that provides good selectivity with respect to the material of the thin encapsulation layer 31 (here amorphous Si), such as a chlorine-containing etchant (Cl 2 , BCl 3 , etc.).

[0067] Reference Figure 1H , a second chemical etching is performed, which is suitable for removing the protective segments 51 made of amorphous carbon and is therefore used to release the surface of the getter gas portions 52. The chemical etching here is a dry chemical etching, the etchant of which is, for example, oxygen present in the plasma. Since this dry chemical etching is isotropic, the integrity of the free structure is preserved, while facilitating the entry of the etchant into the cavity 2 through the first vent 32 and the second vent 33. As a result, the getter segments 52 are released, i.e. they have released (uncoated) surfaces and are therefore exposed to the atmosphere of the cavity 2. They are kept suspended above the readout substrate 10 at the outside by a thin encapsulation layer 31. Here, each of the getter segments 52 has a released lower surface and an upper surface, thereby increasing the total effective surface area of ​​the getter material in the cavity 2.

[0068] Reference Figure 1I, a sealing layer 34 is deposited on the thin encapsulation layer 31 with sufficient thickness to ensure that the various vents 32, 33 are sealed, i.e. blocked. The sealing layer 34 is transparent to the electromagnetic radiation to be detected and can be made of germanium with a thickness of about 1.7 μm. An antireflection layer (not shown) can also be deposited, which allows optimizing the transmission of electromagnetic radiation through the encapsulation structure. The antireflection layer can be made of zinc sulfide with a thickness of about 1.2 μm. A sealed cavity 2 under vacuum or low pressure is obtained, in which the thermal detector 20 and the getter segment 52 are accommodated, which is suspended above the readout substrate 10 and maintained by the thin encapsulation layer 31.

[0069] The manufacturing method according to the invention thus allows an improvement in the protection of the getter segments 52 against wet etching during the step of removing the mineral sacrificial layers 61, 62. In particular, in the configuration of the aforementioned document EP3239670A1, in which the mineral sacrificial layer 61 is a silicon oxide deposited on a protective layer, the inventors have observed a potential degradation of this protective layer when it is made of amorphous carbon and the silicon oxide is obtained in particular using a tetraethyl orthosilicate (TEOS) compound, which could lead to degradation of the getter segments 52. In contrast, here, the protective segment 51 made of amorphous carbon is deposited after the creation of the mineral sacrificial layers 61, 62, so that it is protected from any degradation associated with the step of creating these mineral sacrificial layers 61, 62.

[0070] Furthermore, the protection of the getter segment 52 from wet etching is improved, as long as potential defects of the protective segment 51 covering the getter segment 52 are avoided. In particular, in the configuration of document EP3239670A1, in which a protective layer is deposited on the getter segment 52, the inventors have observed that when the protective layer is made of amorphous carbon, defects may occur in the coverage of the side surfaces of the getter segment 52. In contrast, here, the protective segment 51 is planar and covers only the lower and / or upper surface of the getter segment 52, but not its side surfaces, thereby reducing or even avoiding the risk of coverage defects.

[0071] Furthermore, document EP2141117A1 describes a configuration in which a thermal detector is encapsulated in a sealed cavity. The getter segment is produced on a sacrificial layer and protected by an intermediate protective layer. The problems associated with the use of protective materials made of amorphous carbon and mineral sacrificial materials are not mentioned. Furthermore, the document describes a protective layer covering the upper surface of the sacrificial layer and the sides of the sacrificial layer, and the protective layer extends onto the substrate at the boundary of the sacrificial layer. This configuration results in a packaging structure with a larger footprint, while the manufacturing method described allows the small footprint described in document EP3239670A1 to be retained. In any case, the getter segment in document EP3239670A1 is constructed so that it only partially covers the protective layer. In contrast, in the method according to the present invention, the protective layer 41 and the getter layer 42 are constructed together to form a getter pad 50. Therefore, the getter segment 52 completely covers the upper surface of the protective segment 51.

[0072] Furthermore, the protective layer described in document EP 2 141 117 A1 is not continuously flat over its entire area, so if it is made of amorphous carbon, coverage defects may occur, leading to possible degradation of the getter segment, especially when it is located near the vertical portion of the protective layer. This situation is avoided in the manufacturing method according to the present invention.

[0073] Figures 2A to 2D The various steps of a method for manufacturing a detection device 1 according to a different embodiment are shown. This variant differs from the above-described method primarily in that a lateral overetching of the protective segments 51 of one or more getter pads 50 is performed. Only certain steps are described in detail here; the other steps are identical or similar to the above-described steps.

[0074] Reference Figure 2A , one or more getter pads 50 are produced on the mineral sacrificial layer 62, which are positioned away from the optically active thermal detector 20 in the XY plane and are arranged facing the compensation detector 3. The mask 65 covers only the upper surface of the getter pads 50, but not the side surfaces of the getter pads. The protective segment 51 and the getter segment 52 have substantially the same dimensions in the XY plane, so that the getter pads 50 have substantially vertical sides (within manufacturing tolerances).

[0075] Reference Figure 2B , an isotropic dry etch is performed, for example, in an oxygen plasma, so as to cause a slight lateral overetching of the sides of the protective segment 51, rather than a slight lateral overetching of the sides of the getter segment 52. As a result, the dimensions of the protective segment 51 in the XY plane are smaller than the dimensions of the getter segment 52. This two-dimensional topology of the sides of the getter pad 50 (along the Z axis) is utilized to improve the mechanical retention of the getter segment when the getter segment 52 is suspended after the dry chemical etching step.

[0076] Reference Figure 2C , resulting in a thin encapsulation layer 31. In this example, for clarity, the thin insulating layer is not shown on the sides of the getter pad 50. It can be present and does not extend above the getter pad 50. Therefore, the upper wall 31.1 of the thin encapsulation layer 31 extends to cover the sides of the two-dimensional topology of the getter pad 50, so that the mechanical holding area is larger than Figures 1A to 1I .

[0077] Reference Figure 2D After the various vents 32, 33 and holes 53 have been produced and the mineral sacrificial layers 61, 62 have been removed by wet etching and the protective segment 51 has been removed by dry etching, a thin sealing layer 34 is deposited. The package structure 30 thus obtained is here compared with the reference Figure 1I The described encapsulation structure differs substantially in that the thin encapsulation layer 31 here covers the outer boundaries of the lower and upper surfaces of the getter segments 52 because of the initial two-dimensional topology of the sides of the getter pad 50. Thus, the mechanical holding of the thus suspended getter segments 52 is improved.

[0078] Figure 3 is a schematic top partial view of an arrangement example of the thermal detector 20 , the compensation detector 3 and the getter segment 52 .

[0079] Each of the thermal detectors 20 comprises an absorption film 23, which is suspended above the readout substrate 10 by means of an anchoring post 21 and a retaining and thermally insulating arm 22. A support post 31.3 is arranged here so as to rest on a portion of the anchoring post 21. Here, one anchoring post 21 is divided into two parts along the X-axis and the Y-axis to accommodate the support post 31.3. The first ventilation opening 32 is arranged here facing the other anchoring post 31.3. Other arrangements of the first ventilation opening 32 are of course possible.

[0080] Each of the compensating detectors 3 comprises a membrane 3.3 which is substantially identical to the absorbing membrane 23, but is not intended to receive the electromagnetic radiation to be detected. These membranes 3.3 are suspended above the readout substrate 10 by means of anchoring posts 3.1. In this configuration, the membranes 3.3 are not thermally insulated from the readout substrate 10 by means of retaining arms. The support posts 31.3 are here arranged to lie on the anchoring posts 3.1. The getter segment 52 here faces the membrane 3.3 and has dimensions selected to shield the membrane from electromagnetic radiation. The vent 33 is here located in the center of the getter segment 52.

[0081] Thus, the effective surface area of ​​one or more getter segments 52 can be large while limiting the footprint and size of the package structure. Stacking multiple getter segments 52 on top of each other allows the effective surface area of ​​the getter material to be increased without having to increase the size of the sealed cavity 2.

[0082] Figures 4A to 4CThe various steps of the method for manufacturing a detection device 1 according to another variant embodiment are shown. Figures 1A to 1I The method described is different mainly in that a second thin sealing layer 54 is used to block the second ventilation opening 33. Only certain steps are described in detail here, while the other steps are the same or similar to the above steps.

[0083] Reference Figure 4A , resulting in an overall similarity to the reference Figure 1E However, instead of continuing to remove the mineral sacrificial layers 61, 62, a self-aligned hole 53 is created extending through the getter pad 50 from the second vent 33. In this example, the hole 53 is not a through hole, but leads to the lower protective segment 51.1.

[0084] Reference Figure 4B A thin sealing layer 54 is deposited on the thin encapsulation layer 31 so as to block the second vent 33. This sealing layer 54 is preferably partially etched so as to leave only a portion covering the getter pad 50, and in particular when it is made of a material that is opaque to the electromagnetic radiation to be detected, the portion facing the thermal detector 20 is removed. Thus, the vent 32 is not blocked by the thin sealing layer 54.

[0085] Reference Figure 4C After the mineral sacrificial layers 61, 62 have been removed by wet etching and the protective segment 51 has been removed by dry etching, a thin sealing layer 34 is deposited in order to block the ventilation opening 32. The package structure 30 thus obtained is here compared with the reference Figure 1I The package structure described is essentially different because it comprises a second thin sealing layer 54 covering the initial getter pad 50 , which second thin sealing layer is different from the thin sealing layer 34 and preferably does not face the thermal detector 20 .

[0086] Figures 5A to 5C The various steps of the method for manufacturing a detection device 1 according to another variant embodiment are shown. Figures 1A to 1I The method described differs mainly in that the detection device 1 does not include compensation detectors 3 (although it may include some) and in that the getter pad 50 includes a single protective segment 51 made of amorphous carbon and a single getter segment 52. Only certain steps are described in detail here, the other steps being identical or similar to those described above.

[0087] Reference Figure 5AThe getter pad 50 is created by the getter stack 40 so that it is positioned away from the optically active thermal detector 20 in the XY plane and is located only on the upper surface of the mineral sacrificial layer 62. It is formed by a protective segment 51 made of amorphous carbon, which is located on the flat upper surface of the mineral sacrificial layer 62 and is in contact with it. The getter segment 52 covers only the upper surface of the protective segment 51 and is therefore not in contact with its sides or with the mineral sacrificial layer 62.

[0088] Reference Figure 5B The thin encapsulation layer 31 is produced such that the upper wall 31.1 covers the upper surface of the mineral sacrificial layer 62 and the getter pad 50, and the peripheral wall 31.2 extends into the groove and contacts the mineral sacrificial layers 61, 62. A vent 32 is produced through the thin encapsulation layer 31 so that it opens into the mineral sacrificial layer 62. It is remote from the getter pad 50.

[0089] Reference Figure 5C The mineral sacrificial layers 61, 62 are removed by wet etching, here in HF vapor. The protective segment 51 has a released lower surface, but the getter segment 52 remains protected during this step. Next, the protective segment 51 made of amorphous carbon is removed by dry etching (here in oxygen plasma) to release the lower surface of the getter segment 52. A thin sealing layer 34 and an antireflection layer are then deposited.

[0090] Figures 6A to 6C The various steps of a method for manufacturing a detection device 1 according to another embodiment variant are shown. This variant differs from the above-described variant primarily in that the encapsulation structure includes a peripheral wall made of a mineral material. This embodiment variant is described in particular in French patent application FR2003858, filed on May 16, 2020, which is incorporated herein by reference.

[0091] More precisely, if Figure 6C As shown, the peripheral wall 35 which continuously surrounds the thermal detector 20 and here the compensation detector 3 and thus laterally delimits the cavity 2 is no longer integrally formed with and made of the same material as the upper wall 31.1 of the encapsulation layer 31. In other words, it is not part of the encapsulation layer 31. It is made of a different material, here a mineral material, insofar as it consists of unetched sections of the mineral sacrificial layers 61 and 62.

[0092] Figure 6A shows a similar Figure 4A The steps described above are similar. The difference is that encapsulation layer 31 does not include a peripheral wall extending through sacrificial layers 61 and 62 to contact substrate 10. Instead, it includes only upper wall 31.1 and support pillars 31.3. This results in vents 32 located only in central region Zd and vents 33 forming holes 53. Holes 53 are not through-holes but instead open into lower protective segment 51.1.

[0093] Specifically, the surface of the substrate 10 is divided into a plurality of regions:

[0094] a central zone Zd, called the detection zone, in which the matrix of (sensitive) thermal detectors 20 (i.e. detection pixels) is located. The surface of the readout substrate 10 in the detection zone Zd is intended to be completely free of the mineral sacrificial layers 61 , 62 so as not to be covered by the peripheral wall 35 ;

[0095] an intermediate zone Zr, called reinforcement zone, which continuously surrounds the detection zone Zd in the XY plane and in which the virtual detector 3 can be found. It is intended to be covered by a peripheral wall 35;

[0096] A peripheral zone Zp which continuously surrounds the reinforcement zone Zr in the XY plane and in which the upper wall 31 . 1 of the thin encapsulation layer 31 is intended to extend above the peripheral wall 35 and to be in contact therewith.

[0097] Reference Figure 6B A chemical etching process is performed, which is suitable for partially removing the mineral sacrificial layers 61 , 62 through the vents 32 . The chemical etching process is a wet etching process in an acidic medium (eg hydrofluoric acid in the gas phase). The products of the chemical reaction are discharged through the vents 32 .

[0098] Because the ventilation opening 32 is positioned only toward the detection zone Zd, the etchant completely removes the sacrificial mineral layers 61, 62 located in the detection zone Zd, but chemical etching is performed so that the etchant does not etch the peripheral sections of the sacrificial mineral layers 61, 62 extending around the detection zone Zd. The unetched sections of the sacrificial mineral layers 61, 62, on which the upper section 31.1 of the thin encapsulation layer 31 lies, define the peripheral zone Zp. This forms the peripheral wall 35.

[0099] The peripheral wall 35 includes transverse grooves, which widen the cavity 2 vertically, i.e., it has a shape that is flared in the +Z direction. The dimensions of the cavity 2 in the XY plane are larger near the upper section 31.1 than near the released surface of the readout substrate 10. This etch profile of the mineral sacrificial layers 61, 62 is obtained when the sacrificial layer is made of a mineral material and the etching is a chemical etching in an acidic medium in a confined medium.

[0100] Next, as described above, the protection segment 51 located on the side of the getter segment 52 is removed by dry etching.

[0101] Reference Figure 6C, and then a sealing layer 34 is deposited that will block the vents 32 and 33. Thus, the reinforcement pillars 31.3 can be present in the intermediate region Zr and located on the substrate 10. In this example, they are located on the substrate 10 indirectly, here via the pillars 21 of the virtual detector 3. As a variant, they can be located directly on the substrate 10 by vertically passing through the peripheral wall 35 in contact with the substrate 10. In any case, the presence of the reinforcement pillars 31.3 in the intermediate region Zr allows the mechanical strength of the package structure 30 to be improved, as long as they can be in contact with the peripheral wall 35 and at least partially pass through the peripheral wall 35, which ensures a better transmission of mechanical stresses between the package structure 30 and the substrate 10.

[0102] In this variant embodiment, the mechanical strength of package structure 30 on substrate 10 is increased, as long as contact with substrate 10 is ensured by peripheral wall 35 having a lateral dimension greater than peripheral wall 31.2. Therefore, the risk of package structure 30 bonding to substrate 10 is limited.

[0103] 7A to 7C The various steps of the method for manufacturing a detection device 1 according to another variant embodiment are shown. Figures 6A to 6C The described variant differs essentially in that the holes 53 are through-holes, allowing the sacrificial mineral material of the layers 61 and 62 to be removed through the ventilation openings 33 in addition to the ventilation openings 32 .

[0104] therefore, Figure 7A The following steps are shown, wherein the vent 32 is produced facing the sensitive detector 20 and the vent 33 is produced above the getter pad 50. The hole 53 is made as a through hole and opens into the sacrificial layer 62. It can extend partially into this layer 62. In this example, the detection device does not include any dummy detector 3 below the getter pad 50, but as a variant, it can include some (e.g. Figure 6A shown).

[0105] Figure 7B The step is shown in which the sacrificial layers 61 and 62 are partially removed by wet etching in an acidic medium, thereby forming the peripheral wall 35. The mineral sacrificial material is removed here through the ventilation openings 32 and 33.

[0106] Figure 7C The step of depositing a sealing layer 34 on the upper wall 31 . 1 to block the ventilation openings 32 and 33 is shown.

[0107] In this variant, the peripheral wall 35 is arranged laterally away from the sensitive detector 20 and the getter pad 50 , as long as the vents 33 participate in removing the mineral sacrificial material of the layers 61 and 62 .

[0108] A specific embodiment has just been described. Various modifications and variations will be apparent to those skilled in the art. Various variations described above may be combined, particularly with respect to the presence or absence of a compensation detector, the number of guard segments 51 and getter segments 52 in each getter pad 50, the number and arrangement of getter pads 50, and the like.

Claims

1. A method for producing a device (1) for detecting electromagnetic radiation, the method comprising the following steps: o producing at least one thermal detector (20) for detecting electromagnetic radiation, said at least one thermal detector being located on a substrate (10) and covered by at least one mineral sacrificial layer (62) made of a mineral material, said at least one mineral sacrificial layer being removable by a first chemical etch; o Producing at least one pad, referred to as a getter pad (50), which: extending partially over the mineral sacrificial layer (62) and arranged remote from the thermal detector (20) in a plane parallel to the substrate (10), formed by a stack of segments (51, 52) of thin planar layers parallel to one another, comprising a protective segment (51.1) made of amorphous carbon and at least one getter segment (52.1) made of a getter material, said protective segment being removable by a second chemical etch and being in contact with said mineral sacrificial layer (62), said at least one getter segment being in contact with the protective segment (51.1); o producing a thin encapsulation layer (31) extending above the thermal detector, said thin encapsulation layer comprising an upper portion (31.1) located on a mineral sacrificial layer (62) and covering the upper surface and side walls of the getter pad (50); o creating at least one first vent (32) through the thin encapsulation layer (31), the at least one first vent being located away from the getter pad (50) in a plane parallel to the substrate (10) and leading to the mineral sacrificial layer (62); o removing the mineral sacrificial layer (62) by a first chemical etch, thereby releasing the surface of the protective segment (51); o removing the protective segment (51) by a second chemical etch, thereby releasing the surface of the getter segment (52); o A thin sealing layer (34) is deposited on the thin encapsulation layer (31) so as to block at least the first vent (32).

2. The manufacturing method according to claim 1, comprising the step of producing at least one compensation detector (3) not intended for receiving electromagnetic radiation to be detected, the getter pad (50) being arranged facing the compensation detector (3).

3. The manufacturing method according to claim 2, wherein a plurality of thermal detectors (20) and compensation detectors (3) are produced, and at least one getter pad (50) is arranged facing the compensation detector (3).

4. A manufacturing method according to any one of claims 2 and 3, wherein each of the thermal detector (20) and the compensation detector (3) comprises a membrane (23, 3.3) suspended above the substrate by an anchoring column (21, 3.1), and the thin encapsulation layer (31) comprises at least one support column (31.3), which is integrally formed with the upper part (31.1) and extends from the upper part (31.1) to be located on the anchoring column (21, 31.1).

5. The manufacturing method according to claim 4 comprises a step of producing a layer (64) made of electrically insulating material, said layer being arranged between and in contact with the support column (31.3) and the anchor column (21, 3.1).

6. The manufacturing method according to any one of claims 1 to 5, wherein After the step of producing the thin encapsulation layer (31), the thin encapsulation layer (31) extends continuously above and around the thermal detector (20) and is formed by the upper part (31.1) and the surrounding part (31.2) formed in one piece, the surrounding part (31.2) of the thin encapsulation layer (31) extending into the groove produced through the mineral sacrificial layer (62) and contacting its side walls, and the surrounding part (31.2) is located on the substrate.

7. The manufacturing method according to any one of claims 1 to 5, wherein: o during production of the thermal detector (20), the thermal detector is located on a first mineral sacrificial layer (61), the thermal detector (20) and the first mineral sacrificial layer (61) being covered by a second mineral sacrificial layer (62), the first mineral sacrificial layer and the second mineral sacrificial layer (61, 62) being made of a mineral material that can be removed by a first chemical etching; o The first ventilation opening (32) is arranged facing the thermal detector (20), or facing a matrix of thermal detectors (20) where appropriate; During the first chemical etching, which is a wet etching in an acidic medium, the first and second mineral sacrificial layers (61, 62) are partially removed through the first vent (32), the unetched sections of the first and second mineral sacrificial layers (61, 62) forming a peripheral wall (35) surrounding the thermal detector (20) in a plane parallel to the substrate (10), and the upper part (31.1) is located on the peripheral wall.

8. The manufacturing method according to claim 7, wherein: After the first chemical etching, the peripheral wall (35) comprises a transverse groove which causes the cavity (2) to widen vertically parallel to the readout substrate (10) between the readout substrate (10) and the upper part (31.1), the transverse groove defining a middle region (Zr) of the surface of the readout substrate (10) surrounding the thermal detector.

9. The manufacturing method according to claim 8 comprises a step of producing reinforcement columns (31.3) for reinforcing the thin encapsulation layer (31), said reinforcement columns being arranged separately from one another in an intermediate region (Zr) around the thermal detector (20) and extending from said upper part (31.1) to be located on the readout substrate (10).

10. The manufacturing method according to any one of claims 1 to 9, wherein The getter pad (50) includes a plurality of getter segments (52) stacked along an axis perpendicular to the substrate (10), each of the plurality of getter segments being disposed between two protection segments (51).

11. The manufacturing method according to any one of claims 1 to 10, wherein The getter segment (52) completely covers the surface of the protective segment (51) opposite to the substrate (10).

12. The manufacturing method according to claim 11, wherein: During the step of producing the first vent (32), at least one second vent (33) is produced through the thin encapsulation layer (31) so as to lead to an upper protective segment (51.3) covering the getter segment (52), and then, after the step of removing the mineral sacrificial layer (62), a hole (53) is produced from the second vent (33) so as to lead to a lower protective segment (51.1) on which the getter segment (52) is located.

13. The manufacturing method according to claim 12, wherein: A second thin sealing layer (54) is deposited to block the second vent (33), the second thin sealing layer (54) being different from the thin sealing layer (34) blocking the first vent (32).

14. The manufacturing method according to any one of claims 1 to 13, wherein The getter pad (50) comprises a plurality of getter segments (52) and a plurality of protection segments (51), the plurality of getter segments and the plurality of protection segments being stacked along an axis perpendicular to the substrate (10), and wherein lateral overetching of the protection segments (51) is performed selectively relative to the getter segments (52).

15. The manufacturing method according to any one of claims 1 to 14, wherein The mineral sacrificial layer (62) is made of silicon oxide obtained from tetraethyl orthosilicate.

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