Infrared detector and associated production method

Abstract

This infrared detector (10d) comprises: - a base substrate (11) supporting an array of micro-bolometers (19), each micro-bolometer being mounted in suspension above said substrate by means of anchoring nails (14) extending substantially perpendicularly with respect to the base substrate (11); - side walls (13) extending substantially perpendicularly with respect to the base substrate (11); and - an optical window (12) fixed on an upper end of the side walls (13) above the micro-bolometers (19). The base substrate (11), the side walls (13) and the optical window (12) form a vacuum sealed cavity (16) within which the micro-bolometers (19) are present. The infrared detector (10d) also comprises spacers (20) extending plumb with at least 10% of the anchoring nails (14), these spacers (20) also being oriented substantially perpendicularly with respect to the base substrate (11), said spacers (20) forming a stop capable of cooperating with the lower face of the optical window (12), or with the upper end of the anchoring nails (14), and thus limiting the deflections of the optical window (12) and / or of the substrate (11).

Description

[0001] INFRARED DETECTOR AND ASSOCIATED PRODUCTION METHOD

[0002] FIELD OF THE INVENTION

[0003] The invention relates to the field of infrared detection, and in particular detection using micro-bolometers.

[0004] More particularly, the invention relates to an infrared detector produced using the transfer manufacturing of an optical window onto a base substrate. In this context, the invention aims to limit the deflections likely to appear, during vacuum sealing after this transfer, between the optical window and the base substrate. This limitation of the deflections makes it possible in particular to obtain infrared detectors, produced using transfer manufacturing, with a large number of pixels and / or with increased precision.

[0005] Thus, the invention can be implemented in many fields for which infrared images are currently used, such as the fields of aerospace, security, defense, transportation, thermography, industrial inspection, building inspection, leisure, health, etc.

[0006] STATE OF THE ART

[0007] As schematically illustrated in Figure 1, an infrared detector 100 is conventionally in the form of a hermetic cavity 16 integrating a network of micro-bolometers 19. Each micro-bolometer 19 comprises a membrane 15 mounted in suspension on a base substrate 11 by means of anchoring nails 14. The hermetic cavity 16 is generally constituted by an optical window 12 and side walls 13 fixed between the base substrate 11 and the optical window 12.

[0008] A microbolometer 19 is for example designed to have maximum sensitivity over the wavelength range of interest 8-14 micrometers, while being insensitive to flux outside this spectral band. Intrinsically, the uncoated optical window has a transmittance wider than the wavelength range of interest.

[0009] To improve the performance of the infrared detector 100, this optical window is treated or structured with respect to the micro-bolometers 19. Typically, this optical window is intended to attenuate wavelengths between 2 and 8 micrometers, and to form an anti-reflection filter for wavelengths of interest between 8 and 14 micrometers. To do this, the optical window 12 may comprise a first filter 17 and a second filter 18, formed respectively on the lower face and the upper face of the optical window 12.

[0010] Furthermore, for certain applications, it is desired to obtain several distinct responsivity measurements for the same point of an infrared image, for example with several micro-bolometers 19 sensitive in different spectral bands. For example, from several distinct responsivity measurements, it is possible to determine the absolute temperature, i.e. a measurement of the temperature of an object of interest without using a reference object.

[0011] To do this, separate filters can be associated with separate micro-bolometers 19. This embodiment, however, requires limiting the distance between the optical window 12 and the micro-bolometers 19 so that the infrared radiation intended for a specific micro-bolometer 19 mainly passes through the associated filter.

[0012] It may also be sought to limit the distance between the optical window 12 and the microbolometers 19 to simplify the manufacturing process.

[0013] Furthermore, the performance of the infrared detector 100 is also linked to the vacuum level prevailing within the hermetic cavity 16. In order to guarantee the thermal insulation of the microbolometers 19, necessary to achieve the expected performance, the vacuum level in the hermetic cavity 16 must typically be less than 10' 2 mbar. To ensure this vacuum level, in the transfer fabrication technique, the optical window 12 is vacuum sealed on an upper end of the side walls 13 above the base substrate 11 and the microbolometers 19.

[0014] In addition to transfer manufacturing, it is also known to carry out monolithic manufacturing, as described in document US 2002 / 0175284, in which sacrificial layers are implemented to deposit the optical window on the base substrate. In this alternative method to transfer manufacturing, a vent is necessarily used to remove the sacrificial layers.

[0015] Document US 2018 / 0321087 describes yet another type of hybrid manufacturing between monolithic manufacturing and transfer manufacturing. Indeed, in this document, the base substrate is conventionally made with sacrificial layers and, as in transfer manufacturing, the optical window is made separately from the base substrate. However, the optical window incorporates a vent and it is transferred to the base substrate while the sacrificial layers are still present. The welding of the optical window on the base substrate is carried out with these sacrificial layers, and the latter are then necessarily removed by the vent before putting the cavity under vacuum and proceeding with the deposition of a vent sealing layer.

[0016] The invention more specifically aims at manufacturing by transfer, detectable on an infrared detector 100 because the optical window does not include a vent.

[0017] In this manufacturing method, after vacuum sealing the optical window 12 on an upper end of the side walls 13, the vacuum level may cause a deflection of the optical window 12 and / or the base substrate 11, as illustrated in FIG. 1. These deflections reduce the distance Hmin between the optical window 12 and the base substrate 11. Thus, for applications in which the distance between the optical window 12 and the micro-bolometers 19 is small, of the order of 10 to 20 micrometers, if the deflections are too large, typically greater than 10 micrometers, the optical window 12 may come into contact with the micro-bolometers 19, or even destroy or degrade them. Furthermore, the deflection of the optical window 12 can also lead to a degradation of the filtering properties of the filters 17-18 and disturb the optical signal received by the micro-bolometers 19.

[0018] The deflection depends mainly on the vacuum level in the hermetic cavity 16, the external pressure, i.e. the pressure of the medium in which the detector is located, the surface of the infrared detector 100, the thickness Es and the nature of the base substrate 11, and the thickness Ef and the nature of the optical window 12.

[0019] In practice, for an application in which the internal vacuum level and the external pressure in the cavity 16 are known, it is possible to determine the possible surface limits for the infrared detector 100 as a function of the thickness Es and the nature of the base substrate 11 and the thickness Ef and the nature of the optical window 12.

[0020] For example, for an internal void of 10' 2mbar and an external pressure of one bar and a thickness Es of the base substrate 11 of 725 micrometers, it has been determined that it is possible to obtain an infrared detector 100 of 1600 by 1200 pixels with a pixel pitch of 12 micrometers and a distance during sealing between the optical window 12 and the micro-bolometers 19 of 10 micrometers, but not an infrared detector 100 of 2048 by 1536 pixels with a thickness Ef of the optical window 12 of 725 micrometers. Indeed, for an infrared detector 100 of 2048 by 1536 pixels, it has been numerically determined that the deflection of the optical window 12 is greater than 10 micrometers. Under these conditions, the filtering properties of the filters 17-18 are so degraded that the effect of this degradation is visible on the infrared image obtained.

[0021] In another example with a pixel pitch of 12 micrometers and a distance during sealing between the optical window 12 and the micro-bolometers 19 of 10 micrometers, for an internal vacuum of 10' 2 mbar and an external pressure of one bar and a thickness Es of the base substrate 11 of 725 micrometers, it has been determined that it is possible to obtain an infrared detector 100 of 1024 by 768 pixels, but not an infrared detector 100 of 1280 by 1024 pixels with a thickness Ef of the optical window 12 of 300 micrometers. In this example, an infrared detector 100 of 1280 by 1024 pixels would result in a deflection of the optical window 12 greater than 10 micrometers and a visible degradation of the filtering properties of the filters 17-18.

[0022] Thus, the deflection phenomenon limits the possibilities of producing an infrared detector 100 for applications in which the distance between the optical window 12 and the microbolometers 19 is small. The technical problem that the invention seeks to solve therefore consists of proposing an infrared detector having a substrate and an optical window of large size and / or fine size while limiting the deflection.

[0023] STATEMENT OF THE INVENTION

[0024] The invention proposes to address this technical problem by placing spacers between the upper end of at least a portion of the anchor nails and the lower surface of the optical window. These spacers form a mechanical stop capable of opposing these deflections of the optical window and / or the base substrate.

[0025] Thus, the invention relates to an infrared detector comprising: a base substrate supporting an array of micro-bolometers, each micro-bolometer being suspended above said substrate by means of anchoring nails extending substantially perpendicularly relative to the base substrate; side walls extending substantially perpendicularly relative to the base substrate; and an optical window fixed on an upper end of the side walls above the micro-bolometers, the optical window not comprising a vent; the base substrate, the side walls and the optical window forming a vacuum-sealed cavity within which the micro-bolometers are present.According to the invention, the infrared detector also comprises spacers extending directly above at least 10% of the anchoring nails, these spacers also being oriented substantially perpendicularly relative to the base substrate, said spacers forming a stop capable of cooperating with the lower face of the optical window, or with the upper end of the anchoring nails, and thus limiting the deflections of the optical window and / or the substrate.

[0026] The invention thus makes it possible, with the transfer manufacturing, to limit the deflections of the optical window and / or the substrate. With these limited deflections, it is now possible to limit the thickness of the optical window and the base substrate without risking degrading the microbolometers after vacuum sealing of the hermetic cavity. Indeed, the optical window no longer risks coming into contact with the suspended membranes of the microbolometers.

[0027] For space requirements, it is also possible to limit the volume of the hermetic cavity by reducing the distance between the optical window and the base substrate.

[0028] Taking the example of the state of the art, with a pixel pitch of 12 micrometers, a distance during sealing between the optical window and the micro-bolometers of 10 micrometers, an internal vacuum of 10' 2 mbar and an external pressure of one bar, a thickness of the base substrate and the optical window of 725 micrometers, it is now possible with the invention to obtain an infrared detector of 2048 by 1536 pixels.

[0029] To achieve this deflection limiting effect, at least 10% of the anchor nails must be associated with a spacer oriented substantially perpendicular to the base substrate.

[0030] These spacers can be distributed evenly over the anchor nails, for example over all anchor nails or every 2, 4 or 8 anchor nails in a row.

[0031] Alternatively, the spacers may also be distributed according to a non-uniform distribution law which increases the number of spacers at the center of the infrared detector. This embodiment makes it possible to limit the number of spacers by placing a large number of spacers in the areas most sensitive to deflections, typically the center of the infrared detector.

[0032] To ensure mechanical support of the optical window, the spacers may have a cross-sectional area of ​​between 0.5 and 1.5 square micrometers. In addition, the height of the spacers may be at least twice that of the anchor nails, typically a height of 5 micrometers compared to a height of the anchor nails of around 2 micrometers.

[0033] In practice, the contact between the spacers and the optical window or anchor nails is observed after vacuum sealing of the cavity. Thus, before vacuum sealing the cavity, the spacers can be previously fixed on the optical window or on the anchor nails. To obtain vacuum sealing of the cavity, the base substrate and the optical window are placed in a vacuum sealing oven. After sealing, the pressure rises in the sealing oven and deflections of the optical window or the base substrate can then appear.

[0034] Thus, in one embodiment, the spacers are made on the lower face of the optical window and come into contact with the anchoring nails of the base substrate after vacuum sealing of the cavity formed around the micro-bolometers by the base substrate, the side walls and the optical window.

[0035] According to another embodiment, the spacers are made in the extension of the anchoring nails of the base substrate and come into contact with the optical window after vacuum sealing of the cavity formed around the micro-bolometers by the base substrate, the side walls and the optical window.

[0036] In this embodiment, it may be necessary to provide spacer receiving areas on the optical window. Thus, the optical window may be provided with flat areas intended to cooperate with the upper end of the spacers after vacuum sealing of the cavity.

[0037] Indeed, the optical window can be provided on its upper face with a multilayer interference filter or a periodic diffraction grating, and on its lower face, with a multilayer interference filter or a periodic diffraction grating. When the lower face is structured by a periodic diffraction grating, it is advantageous to provide flat areas to receive the spacers and limit possible degradation of the patterns of said grating.

[0038] Alternatively, to protect the patterns of the periodic diffraction grating without limiting the useful surface area of ​​the latter on the underside of the optical window, an upper support, transparent to radiation in the wavelength range of interest of the micro-bolometers, can be formed on the spacers. In this embodiment, the infrared detector comprises an upper support attached to the upper end of the spacers and placed between the spacers and the optical window after vacuum sealing of the cavity. The wavelength range of interest typically corresponds to the range of 8-14 micrometers.

[0039] To produce the spacers on the anchor nails, the invention can implement known additive manufacturing steps using several sacrificial layers.

[0040] Thus, the invention also relates to a method for producing an infrared detector comprising the following steps: depositing and structuring a first sacrificial layer on a base substrate; forming anchoring nails through the first sacrificial layer until reaching the base substrate; forming membranes on the first sacrificial layer and the anchoring nails; depositing and structuring a second sacrificial layer on the membranes and the first sacrificial layer; forming spacers through the second sacrificial layer and in the extension of at least part of the anchoring nails; and removing the sacrificial layers so as to release the micro-bolometers formed by the membranes and the anchoring nails; producing an optical window; forming side walls on the base substrate or the optical window and around the micro-bolometers;the side walls being produced before the removal of the sacrificial layers when they are formed on the base substrate; transfer of the optical window onto the base substrate; and vacuum sealing of the cavity formed by the base substrate, the side walls and the optical window; the spacers forming a stop capable of cooperating with the lower face of the optical window and thus limiting the deflections of the optical window and / or the substrate;when the spacers are made on the underside of the optical window, they come into contact with the anchoring nails of the base substrate after vacuum sealing of the cavity and, when the spacers are made in the extension of the anchoring nails of the base substrate, they come into contact with the optical window after vacuum sealing of the cavity. This process makes it possible to reuse known additive manufacturing steps to produce the spacers on the anchoring nails. It is thus possible to obtain an infrared detector with spacers limiting the deflections while using conventional production tools for infrared detectors.;

[0041] BRIEF DESCRIPTION OF THE FIGURES

[0042] The invention will be better understood from reading the following description, given solely by way of example, and drawn up in relation to the appended drawings, in which identical references designate identical or similar elements, and in which:

[0043] Figure 1 illustrates a schematic sectional view of a state-of-the-art infrared detector;

[0044] Figure 2 illustrates a schematic sectional view of an infrared detector according to a first embodiment of the invention before the step of vacuum sealing the housing;

[0045] Figure 3 illustrates a schematic sectional view of the infrared detector of Figure 2 after the step of vacuum sealing the housing;

[0046] Figure 4 illustrates a schematic sectional view of an infrared detector according to a second embodiment of the invention before the step of vacuum sealing the housing;

[0047] Figure 5 illustrates a schematic sectional view of the infrared detector of Figure 4 after the step of vacuum sealing the housing;

[0048] Figure 6 illustrates a schematic sectional view of an infrared detector according to a third embodiment of the invention before the step of vacuum sealing the housing;

[0049] Figure 7 illustrates a schematic sectional view of the infrared detector of Figure 6 after the step of vacuum sealing the housing;

[0050] Figure 8 illustrates a schematic sectional view of an infrared detector according to a fourth embodiment of the invention before the step of vacuum sealing the housing;

[0051] Figure 9 illustrates a schematic sectional view of the infrared detector of Figure 8 after the step of vacuum sealing the housing; and

[0052] Figures 10 to 16 illustrate a schematic sectional view of the steps for producing a base substrate for the infrared detector of Figure 2.

[0053] DETAILED DESCRIPTION OF THE INVENTION

[0054] To limit the deflection between the optical window 12 and the base substrate 11 of an infrared detector with transfer manufacturing, the invention proposes to use spacers 20. Figures 3, 5, 7 and 9 illustrate four different embodiments for limiting this deflection. In all these embodiments, the base substrate 11 supports an array of microbolometers 19. More precisely, each microbolometer 19 comprises a membrane 15 mounted in suspension above the base substrate 11 by means of anchoring nails 14. For example, each membrane 15 can be mounted on two or four anchoring nails 14 by means of suspension arms aimed at limiting the thermal conduction between the membrane 15 and the base substrate 11. Furthermore, the base substrate 11 can also support a reflector arranged under the membranes 15.

[0055] Microbolometers 19 are conventionally arranged in an array of rows and columns to form the image points, or pixels, of an infrared image.

[0056] In addition to the micro-bolometers 19 shown in FIGS. 2 to 9, other types of micro-bolometers 19 may also be structured on the base substrate 11, for example micro-bolometers thermalized with the substrate, in order to reject a non-useful component of the signal, called common mode, which may be largely predominant. The rejection of this component makes it possible to read the useful signal by making maximum use of the electrical dynamics of the reading circuit.

[0057] In the embodiment of Figures 2 to 7, spacers 20 are formed on several anchoring nails 14 of the detection micro-bolometers 19.

[0058] More specifically, according to the invention, the spacers 20 extend directly above at least 10% of the anchor nails 14 and substantially perpendicularly relative to the base substrate 11. In the example of FIGS. 2 to 7, one microbolometer 19 out of two has spacers 20 fixed on anchor nails 14. Alternatively, the distribution of the spacers 20 can take different forms without changing the invention, provided that at least 10% of the anchor nails 14 are surmounted by spacers 20. Thus, the distribution of the spacers 20 can be uniform. These spacers 20 can in particular be placed on all the anchor nails 14, on one anchor nail 14 out of two, on one anchor nail 14 out of four or even on one anchor nail 14 out of eight, without changing the invention.

[0059] Furthermore, the distribution of the anchor nails 14 may also be non-uniform, i.e., more spacers 20 are placed in certain areas of the infrared detector 10a-10d. Typically, it may be desired to have a spacer 20 positioned on each anchor nail 14 on a substantially central area of ​​the infrared detector 10a-10d, while a peripheral area has a spacer 20 on two or four anchor nails 14. The boundary between the central area and the peripheral area of ​​the infrared detector 10a-10d may be determined such that the central area covers an area twice smaller than the peripheral area, or by any other mathematical definition. In addition to the base substrate 11 and its microbolometers 19, an infrared detector 10a-10d also comprises an optical window 12 fixed on an upper end of side walls 13 and above the microbolometers 19.The side walls 13 may be formed independently of the base substrate 11 and the optical window 12 and fixed to the base substrate 11 before the optical window 12 is transferred. Alternatively, it is possible to structure the base substrate 11 or the optical window 12 so as to form side walls 13.

[0060] For example, these side walls 13 can be made of amorphous silicon allowing the micro-bolometers 19 to be encapsulated laterally. Whatever the technology for forming the side walls 13, they extend substantially perpendicularly relative to the base substrate 11 and allow a vacuum-sealed cavity 16 to be formed by fixing the optical window 12 to the upper ends of said walls.

[0061] To limit the deflections, the spacers 20 form a stop between the anchoring nails 14 of the micro-bolometers 19 and the optical window 12. Conventionally, the optical window 12 is structured by filters making it possible to limit the radiation incident on the micro-bolometers 19.

[0062] In the example of Figures 2 and 3, the optical window 12 is structured with two interference multilayer filters 17 and 18. The total thickness Ef of the optical window 12 therefore corresponds to the thickness of the substrate of this optical window 12 added to the thickness of the two interference multilayer filters 17 and 18. As illustrated in Figure 2, when the optical window 12 is transferred to the base substrate 11, the spacers 20 do not necessarily touch the optical window 12. After vacuum sealing, necessary to form the infrared detector 10a illustrated in Figure 3, a deflection appears and this deflection causes contact between the spacers 20 and the optical window 12. More precisely, in the example of Figure 3, the spacers 20 come into contact with the interference multilayer filter 17 produced on the lower face of the optical window 12.

[0063] The height of the anchoring nails 14 and the spacers 20 makes it possible to define the minimum height Hmin of the cavity 16. Indeed, when the optical window 12 comes into contact with the spacers 20, the deflections of the optical window 12 and / or the base substrate 11 are limited. Typically, the height of the anchoring nails 14 may be between 2 and 2.5 micrometers while the height of the spacers 20 may be between 5 and 10 micrometers. The spacers 20 preferably have a section smaller than the anchoring nails 14. Typically, the anchoring nails 14 may have a section of 2 square micrometers while the spacers 20 may have a cross-section of between 0.5 and 1.5 square micrometers. Given the height and section of the spacers 20, and if they are made of the same material, they are therefore much less thermally conductive than the anchor nails 14.Furthermore, the anchor nails 14 conventionally incorporate metal elements allowing contact to be made with the membrane 15. However, these metal elements are naturally thermal conductors. As regards the spacers 20, they have no electrical conduction function so that they can be made of a thermally insulating material, such as amorphous silicon.

[0064] In the example of Figures 4 and 5, the optical window 12 has a periodic diffraction grating 21 structured on its lower face. This periodic diffraction grating makes it possible, like the interference multilayer filters, to filter part of the incident infrared radiation. However, such a periodic diffraction grating is more sensitive to the risks of deterioration due to contact with a spacer 20. To limit this risk, it is possible to provide flat areas 22, that is to say areas in which no structure of a periodic diffraction grating 21 is produced. These flat areas 22 are intended to cooperate with the upper end of the spacers 20 after vacuum sealing of the cavity 16.

[0065] Typically, with spacers 20 whose section is approximately 1 square micrometer, and an alignment precision of the optical window 12 relative to the base substrate 11 of the order of 2 micrometers when transferring the optical window 12, flat areas of between 3 and 5 micrometers on each side can be produced.

[0066] Thus, for the infrared detector 10b of figure 5, the spacers 20 come into contact with the flat areas 22 of the optical window 12 after vacuum sealing of the cavity 16, so as to limit the possible deterioration of the periodic diffraction gratings 21.

[0067] In the example of Figures 6 and 7, an upper support 23, transparent to infrared radiation in the wavelength range of interest of the micro-bolometers 19, is placed above the spacers 20. This upper support 23 makes it possible to constitute a support zone for the optical window 12 in order to distribute the mechanical pressure of supporting the spacers 20 with the optical window 12. In doing so, the risk of deterioration of a periodic diffraction grating 21 formed on the lower face of the optical window 12 is limited, and it is no longer necessary to provide flat zones. Furthermore, this upper support extends over the entire surface of the micro-bolometers 19 in the example of Figures 6 and 7. Alternatively, this upper support 23 may extend only to the center of the infrared detector 10c.In the example of figures 8 and 9, spacers 20 are fixed on the lower face of the optical window 12 and come into contact with the anchoring nails 14 after vacuum sealing of the cavity 16. This embodiment also makes it possible to guarantee a minimum height Hmin between the optical window 12 and the base substrate 11.

[0068] Figures 10 to 16 illustrate one embodiment of spacers 20 on the anchor nails 14 of a base substrate 11.

[0069] To do this, a first step consists of depositing and structuring a sacrificial layer 30 on a base substrate 11. The anchoring nails 14 are then formed during a second step inside the structuring patterns of the sacrificial layer, as illustrated in FIG. 11. The membranes 15 of the different micro-bolometers 19 are then formed on the sacrificial layer 30 and the anchoring nails 14, as illustrated in FIG. 12.

[0070] A second sacrificial layer 31 is deposited on the membranes 15 and on the first sacrificial layer 30. This second sacrificial layer 31 is also structured in order to define zones for which the spacers 20 are to be produced, and in this case, in the extension of the anchor nails 14, as illustrated in figure 13.

[0071] As illustrated in Figure 14, the spacers 20 can then be formed by deposition of material in the structuring patterns of the second sacrificial layer 31. This deposition can consist of amorphous silicon produced by physical vapor deposition.

[0072] The thin layer of amorphous silicon 43 deposited on the second sacrificial layer 31 can then be removed, for example by reactive ion etching, as illustrated in FIG. 15. Alternatively, it is possible to retain this layer of amorphous silicon 43 to obtain the upper support 23 of FIGS. 6 and 7. If this layer of amorphous silicon 43 is retained, it may be necessary to make vents in this layer of amorphous silicon 43 to allow the removal of the two sacrificial layers 30 and 31.

[0073] Thus, after the removal of the two sacrificial layers 30 and 31 allowing the release of the micro-bolometers 19, the spacers 20 are fixed in the extension of at least part of the anchor nails 14, as illustrated in figure 16.

[0074] To obtain an infrared detector, it is also appropriate to produce the optical window 12, to form the side walls 13 on the base substrate 11 or on the optical window 12, to transfer the optical window 12 onto the base substrate 11 and to vacuum seal the optical window 12 onto the base substrate 11 in order to form the cavity 16. When the side walls 13 are formed on the base substrate 11, these are conventionally formed before the release of the micro-bolometers 19.

[0075] In doing so, the invention makes it possible to obtain a cavity 16 with a fixed minimum height Hmin between the base substrate 11 and the optical window 12 so that it is possible to use a base substrate 11 with a thickness Es less than the thicknesses of the prior art or even an optical window 12 with a thickness Es less than the thicknesses of the prior art while overcoming the constraints of bringing these two elements together. It is also possible to form infrared detectors 10a-10d with detection surfaces greater than the surfaces of the prior art.

[0076] More precisely, with an internal vacuum of 10' 2mbar and an external pressure of one bar, a thickness Es of the base substrate 11 of 725 micrometers, and a thickness Ef of the optical window 12 of 725 micrometers, it is now possible to obtain deflections of less than 10 micrometers by forming an infrared detector 10a- lOd with a resolution greater than or equal to 2048 by 1536 pixels.

[0077] Thus, by limiting the deflection phenomenon, the invention makes it possible to obtain an infrared detector having a substrate and an optical window of large size and / or thin. The invention makes it possible, for example, to produce an infrared detector with separate filters for different micro-bolometers or, more simply, to limit the distance between the optical window 12 and the micro-bolometers 19 to simplify the manufacturing process or limit the size.

Claims

CLAIMS 1. An infrared detector (10a-10d) comprising: a base substrate (11) supporting an array of micro-bolometers (19), each micro-bolometer (19) being suspended above said substrate by means of anchoring nails (14) extending substantially perpendicularly to the base substrate (11); side walls (13) extending substantially perpendicularly to the base substrate (11); and an optical window (12) fixed to an upper end of the side walls (13) above the micro-bolometers (19), the optical window (12) not having a vent; the base substrate (11), the side walls (13) and the optical window (12) forming a vacuum-sealed cavity (16) within which the micro-bolometers (19) are present;characterized in that the infrared detector (10a-10d) also comprises spacers (20) extending directly above at least 10% of the anchoring nails (14), these spacers (20) also being oriented substantially perpendicularly relative to the base substrate (11), said spacers (20) forming a stop capable of cooperating with the lower face of the optical window (12), or with the upper end of the anchoring nails (14), and thus limiting the deflections of the optical window (12) and / or of the substrate (H).; 2. Infrared detector according to claim 1, in which the spacers (20) have a cross-section of between 0.5 and 1.5 square micrometers.

3. Infrared detector according to claim 1 or 2, wherein the spacers (20) are distributed uniformly on the anchor nails (14).

4. Infrared detector according to claim 1 or 2, in which the spacers (20) are distributed according to a non-uniform distribution law which increases the number of spacers (20) at the center of the infrared detector (10a-10d).

5. Infrared detector according to one of claims 1 to 4, in which the spacers (20) are produced on the lower face of the optical window (12) and come into contact with the anchoring nails of the base substrate (11).

6. Infrared detector according to one of claims 1 to 4, in which the spacers (20) are made in the extension of the anchoring nails of the base substrate (11) and come into contact with the optical window (12).

7. Infrared detector according to claim 6, in which the optical window (12) is provided with flat areas (22) cooperating with the upper end of the spacers (20).

8. Infrared detector according to claim 6, wherein the infrared detector (10a-10d) comprises an upper support (23), transparent to radiation in the wavelength range of interest of the micro-bolometers (19), fixed to the upper end of the spacers (20) and placed between the spacers (20) and the optical window (12).

9. Infrared detector according to one of claims 1 to 8, in which the optical window (12) comprises an upper face provided with an interference multilayer filter (18) or a periodic diffraction grating, and a lower face provided with an interference multilayer filter (17) or a periodic diffraction grating (21).

10. Method for producing an infrared detector (10a-10d) according to claim 5, comprising the following steps: depositing and structuring a first sacrificial layer (30) on a base substrate (11); forming anchoring nails (14) through the first sacrificial layer (30) until reaching the base substrate (11); forming membranes (15) on the first sacrificial layer (30) and the anchoring nails (14); depositing and structuring a second sacrificial layer (31) on the membranes (15) and the first sacrificial layer (30); forming spacers (20) through the second sacrificial layer (31) and in the extension of at least part of the anchoring nails (14); and removal of the sacrificial layers (30, 31) so as to release the micro-bolometers (19) formed by the membranes (15) and the anchoring nails (14); production of an optical window (12);forming side walls (13) on the base substrate (11) or on the optical window (12) and around the micro-bolometers (19); the side walls (13) being made before the removal of the sacrificial layers (30, 31) when they are formed on the base substrate (11); transfer of the optical window (12) onto the base substrate (11); and vacuum sealing of the cavity (16) formed by the base substrate (11), the side walls (13) and the optical window (12); the spacers (20) forming a stop capable of cooperating with the lower face of the optical window (12) and thus limiting the deflections of the optical window (12) and / or the substrate (11); the spacers (20) coming into contact with the anchoring nails of the base substrate (11), or with the lower face of the optical window (12) after vacuum sealing of the cavity (16).

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