Bolometer detector

Abstract

The present disclosure relates to a bolometer heat detector (100) comprising a plurality of pixels, each pixel comprising a bolometer heat plate (101) suspended above a substrate (103) by a support pillar (107), the detector further comprising, for at least one of the pixels, a guided mode filter, the guided mode filter comprises a planar waveguide (111) resting on a support pillar (107), and a diffraction grating (113) located on and in contact with the waveguide.

Description

Technical Field

[0001] This description relates generally to the field of electronic devices and, more particularly, to bolometric detectors. Background Art

[0002] Bolometric detectors or imagers operating in the infrared range have been proposed. For example, such detectors are capable of capturing infrared radiation in a wavelength range between a few micrometers and a few hundred micrometers, for example between 3 μm and 20 μm, or more precisely between 7 μm and 14 μm (the “Long Wave InfraRed (LWIR)” band).

[0003] Among the existing bolometric detectors, in particular multispectral detectors have been proposed. Unlike so-called "broadband" or "full-band" detectors, which are suitable for forming a single image of a scene by utilizing their entire spectral sensitivity range, multispectral detectors are able to produce several images of the same scene by utilizing different bands or sub-ranges within their spectral sensitivity range. This enables, for example, a multispectral detector to determine the temperature of several points in the scene to be imaged with almost no assumptions about the emissivity (absolute thermal imaging). The information acquired by a multispectral bolometric detector can also be used to detect or distinguish chemical substances present in the scene. An example of the application of this technology is gas detection, for example detecting gas leaks on industrial plants.

[0004] Multispectral bolometric detectors have been proposed, comprising a filter wheel placed opposite a bolometric sensor adapted to acquire an image of each filter on the wheel. However, these detectors are bulky and require the scene to remain relatively stationary or constant during the image acquisition time. Furthermore, more compact multispectral bolometric detectors are also known, comprising a set of optical filters arranged opposite the bolometric sensor, some filters being adapted to transmit incident radiation mainly in a first wavelength range to some bolometers of the sensor, and other filters being adapted to transmit incident radiation mainly in at least one second wavelength range different from the first wavelength range to other bolometers of the sensor. In this case, for each pixel, each filter may comprise an element located inside the quarter-wave cavity of the pixel, placed at the absorption of the pixel or offset above the pixel. The latter case avoids the need to introduce modifications affecting the bolometric pixel film or to add new elements to the quarter-wave cavity. This makes it easier to adapt the known methods for producing bolometric pixels to the production of such detectors.

[0005] One proposed solution for filtering the above-mentioned pixels is based on the so-called "guided mode resonance" principle. A guided mode resonance filter or GMR filter typically comprises a planar waveguide coupled to an amplitude or phase diffraction grating. The planar waveguide is for example formed in a thin layer of high refractive index n (typically greater than 1.5) and transparent in the infrared range, the layer further having a thickness e (e=λ / (2n)) matched to the median wavelength λ of the band of interest. In addition, the diffraction grating is suitable for selectively coupling infrared radiation whose wavelength has a first diffraction order corresponding to the acceptance angle of the waveguide, the period of the diffraction grating allowing the resonant wavelength to be selected. French patent FR 3054318 describes examples of GMR filter dimensions, their coupling to infrared bolometric pixels and embodiments of the assembly.

[0006] The correct operation of the GMR filter is highly dependent on the periodicity of the structure formed by the diffraction grating. In the case of a columnar matrix with a small pixel pitch and whose diffraction grating pattern is individualized for each pixel, such a periodicity can be difficult to achieve. By way of example, in order to produce a resonance centered on 10 μm, the period of the diffraction grating is of the order of 3.5 μm. In the case of a pixel pitch of about 12 μm, the number of patterns per row or column of the diffraction grating is strictly less than 4 for each pixel. In this case, the spectral response of the GMR filter deviates significantly from the ideal case in which the lateral extension of the diffraction grating is assumed to be infinite and has multiple stray resonances. This leads to a deterioration of the performance of the multispectral bolometric detector, in particular to a reduced pixel rejection performance and the appearance of crosstalk phenomena or "optical crosstalk", which tend to limit the efficiency of the temperature reconstruction algorithm, distort the interpretation of the properties of the compounds present in the scene, etc. Summary of the invention

[0007] There exists a need to overcome some or all of the disadvantages of existing bolometric detectors.

[0008] To this end, one embodiment provides a bolometric thermal detector comprising a plurality of pixels, each pixel comprising a bolometric thermal plate suspended above a substrate by a support pillar, and for at least one of the pixels, the detector further comprising a guided mode filter comprising a planar waveguide resting on the support pillar and a diffraction grating located on and in contact with the waveguide.

[0009] According to one embodiment, the guided mode filter comprises a support element resting on a support post.

[0010] According to one embodiment, each supporting element comprises an electrically conductive area, the sides and the bottom of which are coated with an electrically insulating layer.

[0011] According to one embodiment, each supporting element is made of a single dielectric region.

[0012] According to one embodiment, at least two adjacent pixels of the detector comprise a guided mode filter, the planar waveguides of said pixels being optically isolated by conductive areas, the flanks and the bottom of which are coated with an electrically insulating layer.

[0013] According to one embodiment, each supporting element comprises a dielectric region made of a first material, the sides and the bottom of said region being coated with an insulating layer made of a second material different from the first material.

[0014] According to one embodiment, the first material is amorphous silicon.

[0015] According to one embodiment, the second material is aluminum oxide.

[0016] According to one embodiment, at least two adjacent pixels comprise guided mode filters, the planar waveguides of said pixels being optically separated by a conductive region.

[0017] According to one embodiment, the conductive region and the diffraction grating are made of the same material, preferably metal.

[0018] According to one embodiment, the conductive region and the diffraction grating are made of different materials, preferably metal.

[0019] According to one embodiment, the diffraction grating includes a plurality of pads located on and in contact with a top surface of the planar waveguide.

[0020] One embodiment provides a method for manufacturing a bolometric thermal detector as described, the method comprising the following steps:

[0021] a) forming a support pillar and a support plate above a substrate;

[0022] b) depositing a first sacrificial layer on the side of the top surface of the structure;

[0023] c) forming a planar waveguide and a diffraction grating for said at least one pixel;

[0024] d) forming a via through the entire thickness of the first dielectric layer aligned with each support pillar;

[0025] e) depositing a second insulating layer on the sides of the top surface of the structure; and

[0026] f) Depositing a conductive layer on the sides of the top surface of the structure.

[0027] According to one embodiment, step f) is performed after step e).

[0028] According to one embodiment, step f) is performed before step c). BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The foregoing features and advantages, as well as others, will be described in detail in the following description of specific embodiments given by way of illustration and not limitation with reference to the accompanying drawings, in which:

[0030] Figure 1A , Figure 1B , Figure 1C , Figure 1D , Figure 1E , Figure 1F and Figure 1G Successive steps of an exemplary method for manufacturing a bolometric detector according to one embodiment are shown in schematic and partial top, side and cross-sectional views;

[0031] Figure 2A , Figure 2B , Figure 2C , Figure 2D and Figure 2E Successive steps of an exemplary method for manufacturing a bolometric detector according to one embodiment are shown in schematic and partial top, side and cross-sectional views;

[0032] Figure 3A , Figure 3B , Figure 3C , Figure 3D , Figure 3E , Figure 3F , Figure 3G , Figure 3H , Fig. 3I , Figure 3J ,and Figure 3K Successive steps of an exemplary method for manufacturing a bolometric detector according to one embodiment are shown in schematic and partial top, side and cross-sectional views;

[0033] Figure 4A and Figure 4B The schematic diagram and partial side and cross-sectional views show the method for manufacturing FIG. 3A to FIG. 3K The steps in a variation of the method of the bolometric detector shown in ; and

[0034] Figure 5A and Figure 5B is a graph showing the absorption spectrum of a bolometric pixel. . DETAILED DESCRIPTION

[0035] In the various drawings, similar features have been designated by similar references. In particular, structural and / or functional features that are common in the various embodiments may have the same references and may have the same structure, dimensions, and material properties.

[0036] For clarity, only the operations and elements that are helpful for understanding the embodiments described herein are illustrated and described in detail. In particular, the steps for implementing the substrate, bolometric panels, and support pillars are not described in detail because the described embodiments are compatible with common methods for implementing these elements.

[0037] Unless otherwise stated, when referring to two elements being connected together, this means a direct connection without any intermediate elements except conductors, and when referring to two elements being coupled together, this means the two elements may be connected or they may be coupled via one or more other elements.

[0038] In the following disclosure, unless otherwise stated, when referring to absolute position qualifiers, such as terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as terms "above", "below", "higher", "lower", etc., or to qualifiers to orientation, such as "horizontal", "vertical", etc., reference is made to the orientation shown in the figure.

[0039] Unless otherwise indicated, the expressions "around", "about", "substantially" and "approximately" mean within 10%, and preferably within 5%.

[0040] The term "transmittance of a layer" refers to the ratio between the intensity of radiation leaving the layer and the intensity of radiation entering the layer. In the remainder of the specification, a layer or film is said to be opaque to radiation when the transmittance of radiation through the layer or film is less than 10%. In the remainder of the specification, a layer or film is said to be transparent to radiation when the transmittance of radiation through the layer or film is greater than 10%.

[0041] Figure 1A , Figure 1B , Figure 1C , Figure 1D , Figure 1E , Figure 1F and Figure 1G Successive steps of an exemplary method for manufacturing bolometric detector 100 according to one embodiment are shown in schematic and partial top, side and cross-sectional views.

[0042] Figure 1A and Figure 1B They are schematic diagram, partial top view and along Figure 1A A side view and a cross-sectional view of plane AA are shown, which include the steps of forming a matrix of bolometric pixels.

[0043] In the example shown, each pixel comprises a bolometric plate 101, for example a wafer or a piece of wafer, located above a substrate 103. For example, the substrate 103 is made of a semiconductor material, such as silicon. The substrate 103 is, for example, of the CMOS type (complementary metal-oxide-semiconductor). In this case, transistors, contact elements, conductive vias, etc. suitable for driving the matrix pixels and acquiring signals from the pixels (in Figure 1A and Figure 1B (not described in detail) is formed in the substrate 103, for example. Figure 1A and Figure 1B Not described in detail herein, for example, substrate 103 also includes a reflector allowing a quarter-wave cavity to be formed with bolometric plate 101 .

[0044] In the example shown, the layer 105 covers one side of the substrate 103 (the upper surface of the substrate 103, with Figure 1B 104). This layer 105 is, for example, a sacrificial layer intended to be at least partially removed during the method of implementing the bolometric detector 100. By way of example, the layer 105 is a layer made of an electrically insulating material, for example silicon oxide, obtained, for example, via a precursor such as tetraethylorthosilicate (TEOS). In the example shown, the bolometric plate 101 coats the face of the layer 105 opposite to the substrate 103 (the upper face of the layer 105, with Figure 1B orientation).

[0045] In the example shown, support struts 107 for the bolometric panels 101 extend vertically through the thickness of the layer 105, from its upper surface to the substrate 103. The support struts 107 form vertical legs orthogonal to the upper surface of the substrate 103 and are intended to suspend the bolometric panels 101 above the substrate 103 with the support struts 107 resting on the substrate 103 at the end of the steps of manufacturing the bolometric detector 100, for example after removing the layer 105. In the example shown, each bolometric panel 101 has a substantially square perimeter when viewed from above and rests on two support struts 107 arranged near two diagonally opposite corners of the bolometric panel 101. However, this example is not limiting, as the bolometric panels 101 may alternatively have a perimeter of any shape and rest on any number of support struts 107 (for example higher than or equal to two) arranged in any manner. In the example shown, support arms are used to mechanically fix each bolometric panel 101 to the corresponding support strut 107. The support arms further enable bolometric plate 101 to be coupled or electrically connected to substrate 103 so that a signal can be read.

[0046] Figure 1C is along Figure 1AThe partial schematic side view and the cross section shown in plane AA illustrate the structure obtained at the end of subsequent steps in manufacturing bolometric detector 100 .

[0047] During this step, in the previous Figure 1B On one side of the top surface of the structure described, a sacrificial layer 109 is deposited. This layer 109 coats the top and side surfaces of the bolometric plate 101, as well as the portion of the layer 105 that is not coated by the bolometric plate 101. The layer 109 is, for example, a sacrificial layer intended to be at least partially removed during the method of manufacturing the bolometric detector 100. For example, the layer 109 has a thickness between 500 nm and 2.5 μm, for example about 1.5 μm. By way of example, the layer 109 is a layer made of an electrically insulating material, such as silicon oxide, obtained, for example, from a precursor such as tetraethyl orthosilicate. The layer 109 is, for example, made of the same material as the layer 105.

[0048] Furthermore, a dielectric layer 111 is deposited on layer 109 during this step. Figure 1C In the orientation shown, a dielectric layer 111 covers the upper surface of layer 109. Dielectric layer 111 is a dielectric layer intended to form a planar waveguide on bolometric plate 101. Dielectric layer 111 has a refractive index n and a thickness e, for example equal to approximately λ / (2n), where λ denotes the wavelength of interest of bolometric detector 100. By way of example, dielectric layer 111 is made of amorphous silicon and has a thickness e between 500 nm and 2.5 μm, for example equal to about 1.6 μm for the wavelength range λ of interest of bolometric detector 100 between 8 μm and 14 μm.

[0049] Moreover, during this step a conductive layer is deposited on the dielectric layer 111. A diffraction grating 113 is then formed from the conductive layer, for example by photolithography and then selective etching of the conductive layer, stopping on the dielectric layer 111. In the example shown, the diffraction grating 113 comprises a plurality of pads 115, the diffraction grating 113 then being, for example, an "amplitude" diffraction grating. The diffraction grating 113 has, for example, a geometry that is individualized for each pixel, such as a pitch, i.e. the pitch of the diffraction grating 113 may vary from one pixel to another. The conductive layer in which the diffraction grating 113 is formed has, for example, a thickness between 10 nm and 400 nm, for example in the region of 50 nm. The pads 115 have, for example, a thickness substantially equal to the thickness of the conductive layer in which they are formed. By way of example, the conductive layer is made of a metal, for example aluminum, tungsten, gold or silver, or of a metal alloy, for example an alloy based on aluminum and silicon (for example with a silicon content of about 1%).

[0050] Figure 1D is along Figure 1AThe partial schematic side view and the cross section shown in plane AA illustrate the structure obtained at the end of subsequent steps in manufacturing bolometric detector 100 .

[0051] During this step, in the previous Figure 1C On the side of the top surface of the structure described, a layer 117 is deposited. The layer 117 covers the top surface and the side surfaces of the spacer 115 of the diffraction grating 113, as well as the part of the dielectric layer 111 not covered by the spacer 115. For example, the layer 117 has a thickness between 100 nm and 500 nm, for example around 200 nm. By way of example, the layer 117 is made of an electrically insulating material, such as silicon oxide, which is obtained, for example, from a precursor such as tetraethyl orthosilicate. For example, the layer 117 is made of the same material as the layer 109.

[0052] Furthermore, during this step, grooves 119 are formed in the layers 117 and 111. The grooves 119 extend vertically from the upper surface of the layer 117 through the thickness of the layers 117 and 111 to the upper surface of the layer 109. In the example shown, each groove 119 has an annular shape defining an island, when viewed from above, comprising a portion of the dielectric layer 111, a portion of the layer 117 and a portion of the diffraction grating 113 situated opposite one of the bolometric plates 101. The grooves 119 associated with the various bolometric plates 101 may have common portions, for example the grooves 119 form a grid pattern when viewed from above. By way of example, the grooves 119 are formed by a photolithography step, followed by a step for etching the layer 117 and then a step for etching the dielectric layer 111.

[0053] Figure 1E It is along Figure 1A The schematic, partial side view and cross section of plane AA shown illustrate the structure obtained at the end of subsequent steps in manufacturing bolometric detector 100 .

[0054] During this step, a through hole 121 is formed through the layer 109, which is aligned with the support pillar 107. In the example shown, the through hole 121 extends through the entire thickness of the layer 109, i.e., vertically from the upper surface of the layer 109 to the upper surface of the support pillar 107. In the example shown, the through hole 121 has a lateral dimension that is substantially equal to the lateral dimension of the support pillar 107.

[0055] By way of example, the through hole 121 is formed by a method comprising the following consecutive steps:

[0056] a) In the above Figure 1D A layer of a carbonaceous material such as spin-on carbon (SoC) is deposited on one side of the top surface of the described structure;

[0057] b) causing the carbonaceous material to crawl by heating, for example, to a temperature of about 400° C.;

[0058] c) depositing a dielectric layer, for example a mineral layer made of silicon nitride or silicon oxide, which dielectric layer coats the upper surface of the layer of carbonaceous material;

[0059] d) depositing a layer made of photoresist coating the upper surface of the dielectric layer;

[0060] e) forming openings in the dielectric layer by photolithography and then etching through the openings previously formed in the photoresist layer, followed by removal of the photoresist layer, e.g. by stripping;

[0061] f) etching the layer made of carbonaceous material according to a self-aligned process through the opening formed in the dielectric layer during step e), during which step the dielectric layer acts as a hard mask (thin mineral layer), followed by removal of the dielectric layer;

[0062] g) etching layer 109 through the openings formed in the layer of carbonaceous material in step f), stopping on supporting pillars 107 of bolometric plate 101 ; and

[0063] h) Removing the layer made of carbonaceous material, for example by exposure to an oxygen-based plasma.

[0064] Furthermore, during this step, an insulating layer 123 is deposited on one side of the top surface of the structure. The insulating layer 123 allows the bolometer to be isolated from the dielectric layer 111. Figure 1E In the orientation shown, the insulating layer 123 coats the sides and bottom of the through hole 121, the portion of the upper surface of the layer 109 not coated by the dielectric layer 111, the sides of the dielectric layer 111, and the upper surface and sides of the layer 117. The insulating layer 123 has a thickness of, for example, between 20 nm and 200 nm. By way of example, the insulating layer 123 is made of a material that resists subsequent release operations by exposure to hydrofluoric acid in the gas phase, such as aluminum nitride or aluminum oxide. For example, the insulating layer 123 is an aluminum oxide layer, for example formed by atomic layer deposition (ALD), and has a thickness of about 20 nm or 40 nm.

[0065] Figure 1F and Figure 1G Along Figure 1F The schematic and partial top view as well as the side view and the cross-sectional view of the plane AA shown show the structure obtained at the end of the subsequent steps of manufacturing the bolometric detector 100. The diffraction grating 113 and the layers 117 and 123 are Figure 1F are not shown in order not to overload the drawing.

[0066] During this step, in the previous Figure 1E On one side of the top surface of the depicted structure is deposited a layer 125 which, in the example shown, coats the insulating layer 123. The layer 125 fills the grooves 119 and the through holes 121, thereby forming a supporting element or foot for the guided mode resonance filter or GMR filter comprising the waveguide 111 and the diffraction grating 113. The layer 125 also acts as an optical insulating layer between different pixels of the bolometric detector 100. By way of example, the layer 125 is made of a metal, such as tungsten, or a metal alloy.

[0067] Furthermore, during this step, the layers 117 and 125 are thinned, for example by CMP (chemical and mechanical polishing), and the portion of the layer 123 in contact with the upper surface of the layer 117 is removed by the CMP operation. The layer 117 then has a thickness slightly higher than the thickness of the pad 115 of the diffraction grating 113, and only the portion of the layer 125 that fills the trench 119 and the through hole 121 remains.

[0068] Furthermore, during this step, release nozzles 127 are formed in the thickness of layers 117 and 111, for example by photolithography and subsequent etching. Release is then performed, for example by exposure to the gas phase in hydrofluoric acid, for example, so as to remove layers 105, 109 and 117, thereby suspending bolometric plate 101 of detector 100 above substrate 103. In this example, the GMR filters of bolometric detector 100 then rest on support pillars 107 of bolometric plate 101, with the bottom surface of each GMR filter support element being on and in contact with the top surface of the opposing support pillar 107.

[0069] In this example, the portion of layer 125 that remains at the end of the steps of manufacturing bolometric detector 100 is interconnected. The portion of layer 125 acts, for example, as an optical isolator, allowing to limit crosstalk phenomena, or optical crosstalk, between the individual pixels of bolometric detector 100. In the example shown, the supporting element of the GMR filter comprises a conductive region, in this case a portion of layer 125, the sides and bottom of which are coated with an electrically insulating layer, in this case a portion of layer 123.

[0070] In the example shown, the optical isolator is annular when viewed from above. This allows for optimal optical performance.

[0071] Figure 2A , Figure 2B , Figure 2C , Figure 2D and Figure 2E Successive steps of an exemplary method for manufacturing bolometric detector 200 according to one embodiment are shown in schematic and partial top, side and cross-sectional views.

[0072] The method for manufacturing bolometric detector 200 is similar to the method for manufacturing bolometric detector 100 described in detail above. The method for manufacturing bolometric detector 200 differs from the method for manufacturing bolometric detector 100 in that during the method for manufacturing bolometric detector 200, before depositing dielectric layer 111, layer 109 is etched in order to subsequently form a supporting element of the GMR filter.

[0073] Figure 2A is along Figure 1A The partially schematic side view and the cross-sectional view of the plane AA shown show the structure obtained at the end of the steps of manufacturing the bolometric detector 200 comprising the deposited layer 109 previously described with reference to Figure 1A and Figure 1B Describes one side of the top surface of the structure.

[0074] Furthermore, during this step, a through hole 201 is formed in the layer 109, aligned with the support pillar 107. In the example shown, the through hole 201 passes through the entire thickness of the layer 109 and extends vertically from the upper surface of the layer 109 to the upper surface of the support pillar 107. In the example shown, the through hole 201 has a lateral dimension substantially equal to the support pillar 107. The through hole 201 is formed, for example, by photolithography followed by etching, the etching stopping on the top layer of the support pillar 107.

[0075] Figure 2B is along Figure 1A The partial schematic side view and the cross-sectional view of the plane AA shown illustrate the structure obtained at the end of the subsequent steps of manufacturing bolometric detector 200 .

[0076] During this step, a dielectric layer 111 is deposited on the Figure 2A On one side of the top surface of the depicted structure, in the example shown, dielectric layer 111 fills, i.e. completely fills, via 201 and coats the upper surface of layer 109. However, this example is not limiting, as dielectric layer 111 may alternatively coat the sides and bottom of via 201 without filling them.

[0077] Furthermore, during this step, a spacer 115 of a diffraction grating 113 is formed on the upper surface of the dielectric layer 111, for example as previously described with respect to Figure 1C As described.

[0078] Figure 2C is along Figure 1A The partial schematic side view and the cross-sectional view of the plane AA shown illustrate the structure obtained at the end of the subsequent steps of manufacturing bolometric detector 200 .

[0079] During this step, layer 117 is deposited on the Figure 2B Describes one side of the top surface of the structure.

[0080] Furthermore, during this step, a groove 203 is formed in layer 117 and dielectric layer 111. In the example shown, groove 203 extends vertically through the thickness of layers 117 and 111, from the upper surface of layer 117 to the upper surface of layer 109. For example, when viewed from above, groove 203 has an annular shape that defines the portions of layers 111 and 117 that are located in alignment with bolometric plate 101 and the portions of layers 111 and 117 that are located in alignment with support pillars 107. Thus, as previously described with respect to Figures 1A to 1G Unlike the described embodiment, the geometry of the trenches 203 omits support regions, in which case no trenches 203 are located in alignment with support elements of the GMR filter.

[0081] Furthermore, during this step, an insulating layer 123 is deposited on one side of the top surface of the structure. In the example shown, the layer 123 coats the sides and the bottom of the trench 203, as well as the upper surface of the layer 117.

[0082] Figure 2D and Figure 2E Along Figure 2D The schematic and partial top view as well as the side view and the cross-sectional view of the plane AA shown show the structure obtained at the end of the subsequent steps of manufacturing bolometric detector 200. Diffraction grating 113 and layers 117 and 123 are not shown in FIG. Figure 2D to avoid overloading the drawing.

[0083] During this step, layer 125 is deposited on the Figure 2C On one side of the top surface of the structure depicted. In this example, layer 125 coats insulating layer 123. Layer 125 fills trenches 203 and acts as an optical insulating layer between different pixels of bolometric detector 200.

[0084] Furthermore, during this step, layers 117 and 125 are thinned, for example by CMP, and the portion of layer 123 in contact with the upper surface of layer 117 is removed by the CMP operation. Layer 117 then has a residual thickness slightly greater than that of pad 115 of diffraction grating 113, and only the portion of layer 125 that fills trench 203 remains.

[0085] Furthermore, during this step, release orifices 127 are formed, for example by photolithography and subsequent etching, through the thickness of layers 117 and 111. Release is then performed by exposure to the gas phase in hydrofluoric acid, for example, removing layers 105, 109 and 117, thereby suspending bolometric plate 101 of detector 200 above substrate 103.

[0086] In this example, the portion of layer 125 remaining at the end of the steps for manufacturing bolometric detector 200 is interconnected, and the supporting elements of the GMR filter are made entirely of dielectric material, in this particular case the material of layer 111. Optical isolation between the pixels of detector 200 is provided by the portion of layer 125 of the GMR filter.

[0087] Figure 3A , Figure 3B , Figure 3C , Figure 3D , Figure 3E , Figure 3F , Figure 3G , Figure 3H , Fig. 3I , Figure 3J ,as well as Figure 3K Successive steps of an example method for manufacturing bolometric sensor 300 according to one embodiment are shown in schematic and partial top, side, and cross-sectional views.

[0088] The method for manufacturing bolometric detector 300 has common elements with the above-described methods for manufacturing bolometric detectors 100 and 200. These common elements will not be described in detail below.

[0089] Figure 3A is related to the previous Figure 1A Schematic, partial top view of a structure that is the same as or similar to the structure described. Figure 3B and Figure 3C are along Figure 3A Side view and cross-sectional view of planes BB and CC are shown.

[0090] Figure 3D and Figure 3E are along Figure 3A The schematic, partial side view and cross-sectional view of planes BB and CC shown illustrate the structure obtained at the end of subsequent steps in manufacturing bolometric sensor 300 .

[0091] During this step, layer 109 is deposited on one side of the top surface of the structure and grooves 201 are formed to align with support pillars 107 as previously described with respect to Figure 2A Explained.

[0092] Furthermore, during this step, an insulating layer 123 is deposited on one side of the top surface of the structure. In the example shown, the insulating layer 123 coats the sides and the bottom of the trench 201, as well as the upper surface of the layer 109.

[0093] Figure 3F and Figure 3G are along Figure 3AThe schematic diagram, partial side view and cross-sectional view of planes BB and CC shown illustrate the structure obtained at the end of subsequent steps in manufacturing bolometric sensor 300 .

[0094] During this step, the portion of insulating layer 123 that is located in alignment with bolometric plate 101 is removed. Figure 3G In the example shown, portions of the insulating layer 123 coating the bottom and sides of the trench 201 remain.

[0095] Furthermore, during this step, a dielectric layer 111 is deposited on one side of the top surface of the structure. In the example shown, layer 111 coats the portion of insulating layer 123 that remains near support pillars 107, as well as the portion of the upper surface of layer 109 that is not coated with insulating layer 123. Figure 3G In the example shown, the layer 111 fills the trench 201 . However, this example is not limiting, as the layer 111 may alternatively not completely fill the trench 201 .

[0096] Furthermore, during this step, trenches 301 are formed in layer 111 , for example by photolithography followed by etching. In the example shown, trenches 301 extend vertically from the top surface of layer 111 through the entire thickness of layer 111 .

[0097] Figure 3H is a schematic, partial top view showing the structure obtained at the end of subsequent steps in manufacturing bolometric detector 300 . Fig. 3I , Figure 3J and Figure 3k are respectively along Figure 3H Side views and cross-sectional views of planes BB, CC and DD are shown, showing the same structure.

[0098] During this step, in the previous Figure 3F and Figure 3G A conductive layer is deposited on one side of the top surface of the structure described. The diffraction grating 113 is then formed from the conductive layer, for example by photolithography and then selectively etching the conductive layer, stopping on the dielectric layer 111, as previously described in conjunction with Figure 1C In the example shown, the portion 303 of the conductive layer coating the portion of the trench 301 remains after etching. The portion 303 of the conductive layer ensures the mechanical strength of the GMR filter and serves as optical insulation between the pixels of the detector 300 .

[0099] Furthermore, during this step, a release nozzle 127 is formed, for example through the thickness of the portion 303 of the conductive layer coating the bottom of the groove 301 .

[0100] Figure 4A and Figure 4B The schematic diagram and partial side and cross-sectional views show the method for manufacturing FIG. 3A to FIG. 3K Steps in a variation of the method of the bolometric detector 300 shown in FIG.

[0101] Figure 4A and Figure 4B More specifically, the steps for making bolometric thermal detector 400 are shown, which include the steps previously described with respect to Figure 3F and Figure 3G On one side of the top surface of the structure depicted, a metal layer 401 is deposited. In the example shown, the metal layer 401 fills the trench 301. The metal layer 401 is then thinned, for example by CMP, stopping on the dielectric layer 111. At the end of this operation, the metal layer 401 is, for example, flush with the upper surface of the layer 111, and the portion of the metal layer 401 that is located in alignment with the bolometric plate 101 is removed.

[0102] Alternatively, a layer of silicon oxide may be deposited on the upper surface of the dielectric layer 111 before making the trench 301. In this case, the trench 301 extends vertically from the upper surface of the silicon oxide layer through the entire thickness of the silicon oxide layer and the dielectric layer 111. The metal layer 401 is then thinned by CMP, stopping on the silicon oxide layer. The silicon oxide layer is subsequently removed, for example, by chemical etching selective to the material of the dielectric layer 111 and the material of the metal layer 401, for example by removal in the presence of dilute hydrofluoric acid in the case where the layer 111 is made of amorphous silicon and the layer 401 is made of, for example, tungsten, copper or aluminum.

[0103] Furthermore, during this step, a conductive layer is deposited on one side of the top surface of the structure. The diffraction grating 113 is then formed from the conductive layer, for example by photolithography and then selective etching, stopping on the dielectric layer 111, as previously described with respect to Figure 1C In the example shown, a portion 403 of the conductive layer of the coating layer 401 is retained at the end of etching.

[0104] The material of the conductive layer forming the diffraction grating 113 is, for example, the same as the material of the layer 401, and the portion 403 of the conductive layer is described previously with reference to FIG. Figure 4A and Figure 4B The end of the described steps is retained. Alternatively, the layer from which the diffraction grating 113 is formed and the layer 401 may be made of different materials, such as metal.

[0105] Furthermore, during this step, the release nozzles 127 are formed, for example, through the thickness of the metal layer 401 .

[0106] Figure 5A and Figure 5B is a graph showing the absorption spectrum of a bolometric pixel, converting the evolution of the absorption α (in percentage, %) of the bolometric pixel into a function of the wavelength λ (in micrometers, μm) of the incident radiation.

[0107] More specifically, Figure 5A is a graph 500A showing absorption spectra 501A and 503A of two pixels of a conventional bolometric detector, the pixels including different filters. Figure 5B More precisely, diagram 500B shows absorption spectra 501B and 503B of two pixels of one of bolometric detectors 100 , 200 , 300 , and 400 , which pixels include different filters.

[0108] As in Figure 5A and Figure 5B As shown in Figure 1 , one advantage of the bolometric detectors 100, 200, 300 and 400 described above is that they have reduced rejection losses and fewer crosstalk phenomena compared to existing bolometric detectors. In the bolometric detectors 100, 200, 300 and 400, the GMR filter rests on the bolometric support pillars 107, which advantageously allows to maintain a maximum sensitive surface for the bolometric plate 101. Furthermore, the waveguides 111 of the GMR filters of the bolometric detectors 100, 200, 300 and 400 comprise an optical lateral isolation between the different pixels, thus allowing the crosstalk to be limited and the rejection performance to be improved.

[0109] In bolometric detectors 300 and 400, the supporting elements of the GMR filter resting on supporting pillars 107 each comprise a region of dielectric layer 111, the sides and bottom of which are coated with portions of insulating layer 123. In this case, the supporting elements of the GMR filter are made entirely of one or more dielectric materials. In bolometric detector 200, the supporting elements of the GMR filter comprise a single dielectric material.

[0110] Various embodiments and variations have been described. Those skilled in the art will appreciate that certain features of these embodiments may be combined and that other variations will readily occur to those skilled in the art. In particular, although examples of bolometric detectors 100, 200, 300, and 400 using a sacrificial layer of silicon oxide have been described in detail above, the described embodiments are not limited to this case but are more generally applicable to any type of bolometric technology. Furthermore, although the present description uses an example of a bolometric detector suitable for capturing LWIR infrared radiation, this example is not limiting, as the embodiments of the present description are applicable to bolometric detectors capable of capturing any range of infrared radiation.

[0111] Furthermore, although examples of bolometric detectors 100, 200, 300 and 400 comprising a filter for each pixel have been described, embodiments are not limited to these examples. In particular, some pixels of the detector may be filter-free, such as in the case of white pixels or broadband pixels. At least one of the pixels of the detector thus comprises a guided mode filter comprising a planar waveguide resting on a supporting strut of the bolometric plate and a diffraction grating located on and in contact with the waveguide. A person skilled in the art will be able to fabricate such a device from the indications of the above description.

[0112] Finally, actual implementation of the embodiments and variations described herein is within the capabilities of those skilled in the art based on the functional description provided herein.In particular, the described embodiments are not limited to the specific examples of materials and dimensions mentioned in this description.

Claims

1. A bolometric thermal detector (100; 200; 300; 400) comprising a plurality of pixels, each pixel comprising a bolometric thermal plate (101) suspended above a substrate (103) by a supporting pillar (107), the detector further comprising, for at least one of the pixels, a guided mode filter comprising a planar waveguide (111) resting on the supporting pillar (107), and a diffraction grating (113) located on and in contact with the waveguide.

2. The detector (100; 200; 300; 400) according to claim 1, wherein: The guided mode filter comprises a support element resting on the support pillar (107).

3. The detector (100) according to claim 2, wherein: Each support element comprises an electrically conductive region (125) whose sides and bottom are coated with an electrically insulating layer (123).

4. The detector (200) according to claim 2, wherein: Each support element is made of a single dielectric region (111).

5. The detector (200) according to claim 4, wherein: At least two adjacent pixels of the detector comprise the guided mode filter, the planar waveguides (111) of the pixels being optically isolated by a conductive region (125) whose sides and bottom are coated with an electrically insulating layer (123).

6. The detector (300; 400) according to claim 2, wherein: Each support element comprises a dielectric region (111) made of a first material, the sides and bottom of said region being coated with an insulating layer (123) made of a second material different from said first material.

7. The detector (300; 400) according to claim 6, wherein: The first material is amorphous silicon.

8. The detector (300; 400) according to claim 6, wherein: The second material is aluminum oxide.

9. The detector (300; 400) according to claim 6, wherein: At least two adjacent pixels comprise the guided mode filter, the planar waveguides (111) of the pixels being optically isolated by a conductive region (303).

10. The detector (300; 400) according to claim 9, wherein: The conductive region (303) and the diffraction grating are made of the same material, preferably metal.

11. The detector (300; 400) according to claim 9, wherein: The conductive region (303) and the diffraction grating (113) are made of different materials, preferably metal.

12. The detector (100; 200; 300; 400) according to claim 1, wherein: The diffraction grating (113) includes a plurality of pads (115) located on the top surface of the planar waveguide (111) and in contact with the top surface of the planar waveguide (111).

13. A method for manufacturing a bolometric detector (100; 200; 300; 400) according to claim 1, comprising the following steps: a) forming the support pillar (107) and the bolometric plate (101) above the substrate (103); b) depositing a first sacrificial layer (109) on the side of the top surface of the structure; c) forming the planar waveguide (111) and the diffraction grating (113) for the at least one pixel; d) forming a through hole (121; 201) through the entire thickness of the first dielectric layer (109) aligned with each support pillar (107); e) depositing a second insulating layer (123) on the side of the top surface of the structure; and f) Depositing a conductive layer (125) on the sides of the top surface of the structure.

14. The method according to claim 13, wherein: Step f) is carried out after step e).

15. The method according to claim 13, wherein: Step f) is carried out before step c).

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