Bolometric detector

Abstract

Bolometric Detector The present description relates to a bolometric detector (100) comprising a plurality of pixels each comprising a bolometric board (101) suspended above a substrate (103) by support pillars (107), the detector further comprising, for at least one of said pixels, a guided mode filter comprising a planar waveguide (111) resting on the support pillars (107) and a diffraction grating (113) located on and in contact with the waveguide. Figure for abstract: Fig. 1G

Description

Title of the invention: Bolometric detector Technical field

[0001] The present description relates generally to the field of electronic devices, more particularly bolometric detectors. Prior art

[0002] Bolometric detectors or imagers operating in the infrared range have been proposed. Such detectors are for example capable of capturing infrared radiation in a wavelength range between a few micrometers and several hundred micrometers, for example between 3 and 20 pm, for example more precisely between 7 and 14 pm (LWIR band, from the English “LongWave InfraRed” - long wavelength infrared).

[0003] Among existing bolometric detectors, multispectral detectors have in particular been proposed. Unlike so-called "broadband" or "fullband" detectors, adapted to form a single image of a scene by fully exploiting their spectral sensitivity range, multispectral detectors are capable of producing several images of the same scene by exploiting different bands, or sub-ranges, within their spectral sensitivity range. This allows, for example, multispectral detectors to determine, with few assumptions on the emissivity, the temperature in several places of the scene to be imaged (absolute thermography). The information acquired by multispectral bolometric detectors can also be used to detect or distinguish chemical species present in the scene.An example of the application of this technique is gas detection, for example the detection of gas leaks in an industrial installation.

[0004] Multispectral bolometric detectors comprising a filter wheel placed opposite a bolometric sensor adapted to acquire an image for each filter of the wheel have been proposed. These detectors are however bulky and require that the scene remains relatively immobile, or constant, during the image acquisition time. Other multispectral bolometric detectors are also known, more compact and comprising a group of optical filters arranged opposite a bolometric sensor, certain filters being adapted to transmit incident radiation predominantly in a first wavelength range towards certain bolometers of the sensor and other filters being adapted to transmit incident radiation predominantly in at least a second wavelength range, different from the first wavelength range, towards other bolometers of the sensor.Each filter can in this case include, for each pixel, elements located inside a . quarter-wave cavity of the pixel, placed at the level of an absorber of the pixel or offset above the pixel. The latter case avoids introducing modifications impacting the membrane of the bolometric pixel or adding new elements in the quarter-wave cavity. This facilitates the adaptation of known methods for producing bolometric pixels for the production of such detectors.

[0005] A proposed solution for filtering above the pixels is based on the principle known as "guided mode resonance". A guided mode resonance filter, or GMR filter (from the English "Guided Mode Resonance"), 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 adapted to the median wavelength X of the band of interest (e = X / (2n)). Furthermore, the diffraction grating is adapted to selectively couple infrared radiation whose wavelength has a first diffraction order corresponding to the acceptance angle of the waveguide, the period of the diffraction grating making it possible to select the resonance wavelength.French patent FR 3054318 describes an example of dimensioning a GMR filter, its coupling to an infrared bolometric pixel and embodiments of the assembly.

[0006] The correct operation of a GMR filter depends heavily on respecting the periodicity of the structure formed by the diffraction grating. In the case of a bolometric matrix having a small pixel pitch and whose diffraction grating patterns are individualized for each pixel, this periodicity may prove difficult to respect. For example, to produce a resonance centered around 10 pm, the period of the diffraction grating is of the order of 3.5 pm. In the case of a pixel pitch equal to approximately 12 pm, the number of patterns per row or per column of the diffraction grating is then, for each pixel, strictly less than 4. In this case, the spectral response of the GMR filter deviates greatly from an ideal case where the lateral extension of the diffraction grating is assumed to be infinite, and presents multiple parasitic resonances.This leads to a degradation in the performance of the multispectral bolometric detector, resulting in particular in a drop in pixel rejection performance and the appearance of crosstalk phenomena, or "optical crosstalk", tending to limit the effectiveness of temperature reconstruction algorithms, to distort the interpretation of the nature of the chemical compounds present in the scene, etc. Summary of the invention

[0007] There is a need to overcome all or part of the disadvantages of bolo- detectors. existing metrics.

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

[0009] According to one embodiment, the guided mode filter comprises support elements resting on the support pillars.

[0010] According to one embodiment, each support element comprises an electrically conductive region whose sides and bottom are coated with an electrically insulating layer.

[0011] According to one embodiment, each support element consists of a single dielectric region.

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

[0013] According to one embodiment, each support 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 alumina.

[0016] According to one embodiment, at least two adjacent pixels comprise the filter at guided mode, the planar waveguides of said pixels being optically isolated by an electrically conductive region.

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

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

[0019] According to one embodiment, the diffraction grating comprises a plurality of pads located on and in contact with the upper face of the diffraction grating.

[0020] One embodiment provides a method of manufacturing a bolometric detector as described, the method comprising the following steps: a) forming the support pillars and bolometric boards above the substrate; b) depositing a first sacrificial layer on the upper face of the structure; c) forming, for said at least one of said pixels, the planar waveguide and the network diffraction; d) forming vias throughout the thickness of the first dielectric layer directly above each support pillar; e) depositing a second insulating layer on the upper face of the structure; and f) depositing an electrically conductive layer on the upper face of the structure.

[0021] According to one embodiment, step f) is implemented after step e).

[0022] According to one embodiment, step f) is implemented before step c). Brief description of the drawings

[0023] These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which:

[0024] [Fig.lA], [Fig.lB], [Fig.lC], [Fig.lD], [Fig.lE], [Fig.lF] and [Fig.lG] illustrate, by means of top views and side and sectional views, schematic and partial, successive steps of an example of a method for manufacturing a bolometric detector according to one embodiment;

[0025] [Fig.2A], [Fig.2B], [Fig.2C], [Fig.2D] and [Fig.2E] illustrate, by means of top views and side and sectional views, schematic and partial, successive steps of an example of a method for manufacturing a bolometric detector according to one embodiment;

[0026] [Fig.3A], [Fig.3B], [Fig.3C], [Fig.3D], [Fig.3E], [Fig.3F], [Fig.3G], [Fig.3H], [Fig.31], [Fig.3J] and [Fig.3K] illustrate, by means of top views and side and sectional views, schematic and partial, successive steps of an example of a method for manufacturing a bolometric detector according to one embodiment;

[0027] [Fig.4A] and [Fig.4B] illustrate, by means of schematic and partial side and sectional views, a step of a variant of the manufacturing method of the bolometric detector of FIGS. 3A to 3K; and

[0028] [Fig.5A] and [Fig.5B] are graphs illustrating absorption spectra of bolometric pixels. Description of the embodiments

[0029] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

[0030] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed. In particular, the steps of production of the substrate, the bolometric boards and the support pillars have not been detailed, the embodiments described being compatible with the usual methods of producing these elements.

[0031] Unless otherwise specified, when referring to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be connected by means of one or more other elements.

[0032] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures.

[0033] Unless otherwise specified, the expressions “about”, “approximately”, “substantially”, and “of the order of” mean to within 10%, preferably to within 5%.

[0034] The expression "transmittance of a layer" designates a ratio between the intensity of the radiation leaving a layer and the intensity of the radiation entering the layer. In the remainder of the description, a layer or a film is said to be opaque to radiation when the transmittance of the radiation through the layer or the film is less than 10%. In the remainder of the description, a layer or a film is said to be transparent to radiation when the transmittance of the radiation through the layer or the film is greater than 10%.

[0035] [Fig.lA], [Fig.lB], [Fig.lC], [Fig.lD], [Fig.lE], [Fig.lF] and [Fig.lG] illustrate, by means of top views and side and sectional views, schematic and partial, successive steps of an example of a method for manufacturing a bolometric detector 100 according to one embodiment.

[0036] [Fig.lA] and [Fig.lB] are respectively a top view and a side and sectional view along plane AA of [Fig.lA], schematic and partial, of a step comprising the formation of a matrix of bolometric pixels.

[0037] In the example shown, each pixel comprises a bolometric board 101 located above a substrate 103, for example a wafer or a piece of wafer. The substrate 103 is for example made of a semiconductor material, for example silicon. The substrate 103 is for example of the CMOS type (from the English “Complementary Metal-Oxide-Semiconductor”). In this case, transistors, contact recovery elements, conductive vias, etc. (not detailed in figures 1A and 1B), adapted to control the pixels of the matrix and to acquire signals coming from the pixels, are for example formed in the substrate 103. Although this has not been detailed in figures 1A and 1B, the substrate 103 further comprises, for example, a reflector making it possible to form a quarter-wave cavity with the bolometric board 101.

[0038] In the example illustrated, a layer 105 covers one face of the substrate 103 (the upper face of the substrate 103, in the orientation of [Fig. 1B]). The layer 105 is for example a sacrificial layer intended to be eliminated at least partially during the method of producing the bolometric detector 100. By way of example, the layer 105 is a layer made of an electrically insulating material, for example a silicon oxide, obtained for example via a precursor such as tetraethyl orthosilicate (TEOS). In the example shown, the bolometric plates 101 cover the face of the layer 105 opposite the substrate 103 (the upper face of the layer 105, in the orientation of [Fig. 1B]).

[0039] In the example shown, support pillars 107 of the bolometric boards 101 extend vertically in the thickness of the layer 105, from its upper face to the substrate 103. The support pillars 107 form vertical feet orthogonal to the upper face of the substrate 103 and are intended to suspend the bolometric boards 101 above the substrate 103 at the end of the steps of manufacturing the bolometric detector 100, for example after removal of the layer 105, the support pillars 107 resting on the substrate 103. In the example illustrated, each bolometric board 101 has, in top view, a periphery of substantially square shape and rests on two support pillars 107 arranged in the vicinity of two diagonally opposite corners of the bolometric board 101.This example is however not limiting, the bolometric boards 101 being able, as a variant, to have a periphery of any shape and to be supported on any number, for example greater than or equal to two, of support pillars 107 arranged in any manner. In the example shown, support arms make it possible to mechanically secure each bolometric board 101 with the corresponding support pillars 107. The support arms also make it possible to electrically connect or link the bolometric board 101 to the substrate 103 so as to allow a signal to be read.

[0040] [Fig. IC] is a side and sectional view along plane AA of [Fig. 1 A], schematic and partial, illustrating a structure obtained at the end of a subsequent step of manufacturing the bolometric detector 100.

[0041] During this step, a sacrificial layer 109 is deposited on the side of the upper face of the structure previously described in relation to [Fig. 1B]. The layer 109 covers the upper face and the lateral faces of the bolometric plates 101, and parts of the upper face of the layer 105 not covered by the bolometric plates 101. The layer 109 is for example a sacrificial layer intended to be eliminated at least partially during the process of producing the bolometric detector 100. The layer 109 has for example a thickness of between 500 nm and 2.5 pm, for example equal to approximately 1.5 pm. By way of example, the layer 109 is a layer made of an electrically insulating material, for example a 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.

[0042] Furthermore, a dielectric layer 111 is deposited on the layer 109 during this step. In the orientation of [Fig.1C], the dielectric layer 111 covers the upper face of the layer 109. The dielectric layer 111 is a dielectric layer intended to form a planar waveguide above the bolometric plates 101. The dielectric layer 111 has, for example, a refractive index n and a thickness e equal to approximately X / (2n), where / represents the wavelength of interest of the bolometric detector 100. By way of example, the dielectric layer 111 is made of amorphous silicon and has a thickness e of between 500 nm and 2.5 pm, for example equal to approximately 1.6 pm for a range of wavelengths of interest X of the bolometric detector 100 of between 8 and 14 pm.

[0043] Furthermore, an electrically conductive layer is deposited on the dielectric layer 111 during this step. A diffraction grating 113 is then formed from the electrically conductive layer, for example by photolithography then selective etching of the conductive layer with 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, for example a pitch, individualized for each pixel, that is to say that the pitch of the diffraction grating 113 can vary from one pixel to another. The electrically conductive layer in which the diffraction grating 113 is formed has for example a thickness of between 10 and 400 nm, for example equal to approximately 50 nm.The pads 115 have, for example, a thickness substantially equal to that of the conductive layer in which they are formed. For example, the electrically 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 (having, for example, a silicon content of the order of 1%).

[0044] [Fig. 1D] is a side and sectional view along plane AA of [Fig. 1 A], schematic and partial, illustrating a structure obtained at the end of a subsequent step of manufacturing the bolometric detector 100.

[0045] During this step, a layer 117 is deposited on the side of the upper face of the structure previously described in relation to [Fig. 1C]. The layer 117 covers the upper face and the lateral faces of the pads 115 of the diffraction grating 113, and of the parts of the upper face of the dielectric layer 111 not coated by the pads 115. The layer 117 has for example a thickness of between 100 and 500 nm, for example equal to approximately 200 nm. By way of example, the layer 117 is made of an electrically insulating material, for example a silicon oxide, obtained for example from a precursor such as tetraethyl orthosilicate. The layer 117 is for example made of the same material as the layer 109.

[0046] Furthermore, during this step, trenches 119 are formed in the layers 117 and 111. The trenches 119 extend vertically in the thickness of the layers 117 and 111 from the upper face of the layer 117 to the upper face of the layer 109. In the example shown, each trench 119 has, in top view, an annular shape delimiting an island comprising a part of the dielectric layer 111, a part of the layer 117 and a part of the diffraction grating 113 located opposite one of the bolometric plates 101. The trenches 119 associated with the different bolometric plates 101 may comprise common parts, the trenches 119 forming for example a grid, in top view. For example, the trenches 119 are formed by a photolithography step followed by a step of etching the layer 117 and then a step of etching the dielectric layer 111.

[0047] [Fig. 1E] is a side and sectional view along plane AA of [Fig. 1A], schematic and partial, illustrating a structure obtained at the end of a subsequent step of manufacturing the bolometric detector 100.

[0048] During this step, vias 121 are formed in the layer 109, directly above the support pillars 107. In the example illustrated, the vias 121 pass through the entire thickness of the layer 109, i.e. extend vertically from the upper face of the layer 109 to the upper face of the support pillars 107. In the example shown, the vias 121 have lateral dimensions substantially equal to those of the support pillars 107.

[0049] By way of example, the vias 121 are formed by a method comprising the following successive steps: a) deposition of a layer of carbon material, for example applied by spinning ("Spin-on Carbon" - SoC, in English), on the side of the upper face of the structure described above in relation to [Fig.lD]; (b) finishing the carbonaceous material by heating, for example to a temperature equal to approximately 400°C; c) deposition of a dielectric layer, for example a mineral layer of silicon nitride or silicon oxide, coating the upper face of the layer of carbon material; d) depositing a layer of photosensitive resin coating the upper face of the dielectric layer; e) forming openings in the dielectric layer, by photolithography then etching through openings previously formed in the photosensitive resin layer, then removing the photosensitive resin layer, for example by stripping; f) self-aligned etching of the carbon material layer through the openings formed in the dielectric layer during step e), the dielectric layer acting as a hard mask (mineral thin layer) during this step, then removal of the dielectric layer; g) etching the layer 109 through the openings formed in the layer of carbon material during step f) with a stop on the support pillars 107 of the bolometric boards 101, the layer of carbon material acting as a hard mask during this step; and (h) removal of the carbonaceous material layer, for example by exposure to an oxygen-based plasma.

[0050] Furthermore, during this step, an insulating layer 123 is deposited on the side of the upper face of the structure. The insulating layer 123 makes it possible to insulate the bolometers with respect to the dielectric layer 111. In the orientation of [Fig.lE], the insulating layer 123 coats the lateral faces and the bottom of the vias 121, the parts of the upper face of the layer 109 not coated by the dielectric layer 111, the lateral faces of the dielectric layer 111, and the upper face and the lateral faces of the layer 117. The insulating layer 123 has for example a thickness of between 20 and 200 nm. By way of example, the insulating layer 123 is made of a material resistant to a subsequent release operation by exposure to hydrofluoric acid in the vapor phase, for example aluminum nitride or alumina.The insulating layer 123 is for example a layer of alumina, for example formed by atomic layer deposition (ALD), and having a thickness equal to approximately 20 or 40 nm.

[0051] [Fig.lF] and [Fig.lG] are respectively a top view and a side view and in section along the plane AA of [Fig.lF], schematic and partial, illustrating a structure obtained at the end of a subsequent step of manufacturing the bolometric detector 100. The diffraction grating 113 and the layers 117 and 123 have not been represented in [Fig.lF] in order not to overload the drawing.

[0052] During this step, a layer 125 is deposited on the side of the upper face of the structure previously described in relation to [Fig. 1E]. In the illustrated example, the layer 125 covers the insulating layer 123. The layer 125 fills the trenches 119 and the vias 121, thus forming support elements or feet of a guided mode resonance filter, or GMR filter, comprising the waveguide 111 and the dif grating fraction 113. Layer 125 also acts as an optically insulating layer between the different pixels of the bolometric detector 100. For example, layer 125 is made of a metal, for example tungsten, or a metal alloy.

[0053] Furthermore, during this step, the layer 117 and the layer 125 are thinned, for example by CMP (from the English “Chemical and Mechanical Polishing”), the portion of the layer 123 in contact with the upper face of the layer 117 being eliminated by the CMP operation. The layer 117 then has a thickness slightly greater than that of the pads 115 of the diffraction grating 113 and only parts of the layer 125 filling the trenches 119 and the vias 121 are retained.

[0054] Furthermore, during this step, release vents 127 are formed in the thickness of the layers 117 and 111, for example by photolithography then etching. A release by exposure to hydrofluoric acid in the vapor phase is then for example then implemented so as to eliminate the layers 105, 109 and 117, which has the effect of suspending the bolometric plates 101 of the detector 100 above the substrate 103. In this example, the GMR filter of the bolometric detector 100 is then supported on the support pillars 107 of the bolometric plates 101, the lower face of each support element of the GMR filter being on and in contact with the upper face of the support pillar 107 located opposite.

[0055] In this example, the parts of the layer 125 which remain at the end of the manufacturing steps of the bolometric detector 100 are interconnected. The parts of the layer 125 play for example the role of an optical isolator making it possible to limit the phenomena of crosstalk, or “optical crosstalk”, between the different pixels of the bolometric detector 100. In the example shown, the support elements of the GMR filter comprise an electrically conductive region, in this case a part of the layer 125, the sides and the bottom of which are coated with an electrically insulating layer, in this case a part of the layer 123.

[0056] In the illustrated example, the optical isolator has, in top view, an annular shape. This makes it possible to achieve optimal optical performance.

[0057] [Fig.2A], [Fig.2B], [Fig.2C], [Fig.2D] and [Fig.2E] illustrate, by means of top views and side and sectional views, schematic and partial, successive steps of an example of a method for manufacturing a bolometric detector 200 according to one embodiment.

[0058] The method for producing the bolometric detector 200 has similarities with the method for producing the bolometric detector 100 detailed above. The method for producing the bolometric detector 200 differs from the method for producing the bolometric detector 100 in that, in the method for producing the bolometric detector 200, the layer 109 is etched, in order to subsequently form the GMR filter support elements, prior to the deposition of the dielectric layer 111.

[0059] [Fig.2A] is a side and sectional view along plane AA of [Fig. 1A], schematic and partial, illustrating a structure obtained at the end of a manufacturing step of the bolometric detector 200 comprising the deposition, on the side of the upper face of the structure previously described in relation to FIGS. 1A and 1B, of the layer 109.

[0060] Furthermore, during this step, vias 201 are formed in the layer 109, directly above the support pillars 107. In the example illustrated, the vias 201 pass through the entire thickness of the layer 109 and extend vertically from the upper face of the layer 109 to the upper face of the support pillars 107. In the example shown, the vias 201 have lateral dimensions substantially equal to those of the support pillars 107. The vias 201 are for example formed by photolithography then etching, with a stop on the upper layer of the support pillars 107.

[0061] [Fig.2B] is a side and sectional view along plane AA of [Fig. 1A], schematic and partial, illustrating a structure obtained at the end of a subsequent step of manufacturing the bolometric detector 200.

[0062] During this step, the dielectric layer 111 is deposited on the side of the upper face of the structure previously described in relation to [Fig.2A]. In the example shown, the dielectric layer 111 fills, that is to say completely fills, the vias 201 and covers the upper face of the layer 109. This example is however not limiting, the dielectric layer 111 being able, as a variant, to cover the sides and the bottom of the vias 201 without filling them.

[0063] Furthermore, during this step, the pads 115 of the diffraction grating 113 are formed on the upper face of the dielectric layer 111, for example as explained previously in relation to [Fig. 1C].

[0064] [Fig.2C] is a side and sectional view along plane AA of [Fig. 1A], schematic and partial, illustrating a structure obtained at the end of a subsequent step of manufacturing the bolometric detector 200.

[0065] During this step, the layer 117 is deposited on the side of the upper face of the structure previously described in relation to [Fig.2B].

[0066] Furthermore, during this step, trenches 203 are formed in the layer 117 and in the dielectric layer 111. In the example shown, the trenches 203 extend vertically in the thickness of the layers 117 and 111, from the upper face of the layer 117, to the upper face of the layer 109. The trenches 203 have for example, in top view, an annular shape delimiting parts of the layers 111 and 117 located directly above the bolometric board 101, and parts of the layers 111 and 117 located directly above the support pillars 107. Thus, unlike the embodiment previously described in relation to figures 1A to 1G, the geometry of the trenches 203 spares the support zones, no trench 203 being, in this case, located directly above the support elements of the GMR filter.

[0067] Furthermore, during this step, the insulating layer 123 is deposited on the side of the upper face of the structure. In the example illustrated, the layer 123 covers the sides and the bottom of the trenches 203 as well as the upper face of the layer 117.

[0068] [Fig.2D] and [Fig.2E] are respectively a top view and a side and sectional view along plane AA of [Fig.2D], schematic and partial, illustrating a structure obtained at the end of a subsequent step of manufacturing the bolometric detector 200. The diffraction grating 113 and the layers 117 and 123 have not been shown in [Fig.2D] so as not to overload the drawing.

[0069] During this step, the layer 125 is deposited on the side of the upper face of the structure previously described in relation to [Fig.2C]. In the example illustrated, the layer 125 covers the insulating layer 123. The layer 125 fills the trenches 203 and acts as an optically insulating layer between the different pixels of the bolometric detector 200.

[0070] Furthermore, during this step, the layer 117 and the layer 125 are thinned, for example by CMP, the portion of the layer 123 in contact with the upper face of the layer 117 being eliminated by the CMP operation. The layer 117 then has a residual thickness slightly greater than that of the pads 115 of the diffraction grating 113, and only parts of the layer 125 filling the trenches 203 are retained.

[0071] Furthermore, during this step, the release vents 127 are formed in the thickness of the layers 117 and 111, for example by photolithography then etching. A release by exposure to hydrofluoric acid in the vapor phase is then for example subsequently implemented so as to eliminate the layers 105, 109 and 117, which has the effect of suspending the bolometric plates 101 of the detector 200 above the substrate 103.

[0072] In this example, the parts of layer 125 which remain at the end of the manufacturing steps of the bolometric detector 200 are interconnected, and the support elements of the GMR filter are entirely made of a dielectric material, in this case the material of layer 111. The optical isolation between the pixels of the detector 200 is ensured by the parts of layer 125 of the GMR filter.

[0073] [Fig.3A], [Fig.3B], [Fig.3C], [Fig.3D], [Fig.3E], [Fig.3F], [Fig.3G], [Fig.3H], [Fig.31], [Fig.3J] and [Fig.3K] illustrate, by means of top views and side and sectional views, schematic and partial, successive steps of an example of a method for manufacturing a bolometric detector 300 according to one embodiment.

[0074] The method for producing the bolometric detector 300 has elements in common with the methods for producing the bolometric detectors 100 and 200 detailed above. These common elements will not be detailed again below.

[0075] [Fig.3A] is a schematic and partial top view illustrating a structure identical or similar to that previously described in relation to [Fig.1A]. [Fig.3B] and [Fig.3C] are side and sectional views, respectively along planes BB and CC of [Fig.3A], of the structure.

[0076] [Fig.3D] and [Fig.3E] are side and sectional views, respectively along planes BB and CC of [Fig.3A], schematic and partial, illustrating a structure obtained at the end of a subsequent step of manufacturing the bolometric detector 300.

[0077] During this step, the layer 109 is deposited on the side of the upper face of the structure and the trenches 201 are formed directly above the support pillars 107 as explained previously in relation to [Fig.2A].

[0078] Furthermore, during this step, the insulating layer 123 is deposited on the side of the upper face of the structure. In the example illustrated, the insulating layer 123 covers the sides and the bottom of the trenches 201 as well as the upper face of the layer 109.

[0079] [Fig.3F] and [Fig.3G] are side and sectional views, respectively along planes BB and CC of [Fig.3A], schematic and partial, illustrating a structure obtained at the end of a subsequent step of manufacturing the bolometric detector 300.

[0080] During this step, parts of the insulating layer 123 located directly above the bolometric boards 101 are eliminated. In the example shown in [Fig.3G], portions of the insulating layer 123 covering the bottom and the sides of the trenches 201 are retained.

[0081] Furthermore, during this step, the dielectric layer 111 is deposited on the side of the upper face of the structure. In the example shown, the layer 111 coats the parts of the insulating layer 123 which remain in the vicinity of the support pillars 107 as well as parts of the upper face of the layer 109 not coated with the insulating layer 123. In the example illustrated in [Fig.3G], the layer 111 fills the trenches 201. This example is however not limiting, the layer 111 being able, as a variant, not to completely fill the trenches 201.

[0082] Furthermore, during this step, trenches 301 are formed, for example by photolithography then etching, in the layer 111. In the example shown, the trenches 301 extend vertically throughout the thickness of the layer 111 from its upper face.

[0083] [Fig.3H] is a top view, schematic and partial, illustrating a structure obtained at the end of a subsequent step of manufacturing the bolometric detector 300. [Fig.31], [Fig.3J] and [Fig.3K] are side and sectional views, respectively along the planes BB, CC and DD of [Fig.3H], illustrating this same structure.

[0084] During this step, an electrically conductive layer is deposited on the side of the upper face of the structure previously described in relation to Figures 3F and 3G. The diffraction grating 113 is then formed from the electrically conductive layer, for example by photolithography then selective etching of the conductive layer with stop on the dielectric layer 111 as explained previously in relation to [Fig.lC]. In the example shown, parts 303 of the conductive layer coating the bottom and the sides of the trenches 301 remain after the etching. The parts 303 of the conductive layer ensure the mechanical strength of the GMR filter and play a role of optical insulation between the pixels of the detector 300.

[0085] Furthermore, during this step, the release vents 127 are formed, for example in the thickness of the parts 303 of the conductive layer covering the bottom of the trenches 301.

[0086] [Fig.4A] and [Fig.4B] illustrate, by side and sectional views, respectively according to planes BB and DD of [Fig.3H], schematic and partial, a step of a variant of the manufacturing method of the bolometric detector 300 of FIGS. 3A to 3K.

[0087] Figures 4A and 4B illustrate more particularly a step of manufacturing a bolometric detector 400 comprising the deposition of a metal layer 401 on the side of the upper face of the structure previously described in relation to Figures 3F and 3G. In the example shown, the metal layer 401 fills the trenches 301. The metal layer 401 is for example then thinned, for example by CMP, with a stop on the dielectric layer 111. At the end of this operation, the metal layer 401 is for example flush with the upper face of the layer 111, and parts of the metal layer 401 located directly above the bolometric plates 101 are eliminated.

[0088] As a variant, a silicon oxide layer may be deposited on the upper face of the dielectric layer 111 prior to the production of the trenches 301. In this case, the trenches 301 extend vertically from the upper face of the silicon oxide layer throughout the thickness of the silicon oxide layer and the dielectric layer 111. The thinning of the metal layer 401 by CMP is then carried out with a stop on the silicon oxide layer. The silicon oxide layer is subsequently removed, for example by selective chemical etching with respect 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 where the layer 401 is, for example, made of tungsten, copper or aluminum.

[0089] Furthermore, during this step, an electrically conductive layer is deposited on the side of the upper face of the structure. The diffraction grating 113 is then formed from the electrically conductive layer, for example by photolithography then selective etching with stopping on the dielectric layer 111 as explained previously in relation to [Fig.lC]. In the example shown, parts 403 of the conductive layer coating parts of the layer 401 remain at the end of the etching.

[0090] The material of the conductive layer in which the diffraction grating 113 is formed, and of which the parts 403 remain at the end of the step previously described in relation to FIGS. 4A and 4B, is for example identical to that of the layer 401. As a variant, the layer from which the diffraction grating 113 is formed and the layer 401 may be made of different materials, for example metals.

[0091] Furthermore, during this step, the release vents 127 are formed, for example in the thickness of the metal layer 401.

[0092] [Fig.5A] and [Fig.5B] are graphs illustrating absorption spectra of bolometric pixels, reflecting an evolution of the absorption a (in percent, %) of the bolometric pixel as a function of the wavelength X of the incident radiation (in micrometers, pm).

[0093] [Fig.5A] is more precisely a graph 500A illustrating absorption spectra 501A and 503A of two pixels of a conventional bolometric detector, the pixels comprising different filters. [Fig.5B] is more precisely a graph 500B illustrating absorption spectra 501B and 503B of two pixels of one of the bolometric detectors 100, 200, 300 and 400, the pixels comprising different filters.

[0094] As illustrated in Figures 5A and 5B, an advantage of the bolometric detectors 100, 200, 300 and 400 described above is that they have reduced rejection losses and less significant crosstalk phenomena compared to existing bolometric detectors. In the bolometric detectors 100, 200, 300 and 400, the GMR filter rests on the support pillars 107 of the bolometers, which advantageously makes it possible to maintain a maximum sensitive surface for the bolometric plates 101. Furthermore, the waveguide 111 of the GMR filter of the bolometric detectors 100, 200, 300 and 400 comprises optical lateral isolation between the different pixels, thus making it possible to limit crosstalk and improve rejection performance.

[0095] In the bolometric detectors 300 and 400, the support elements of the GMR filter resting on the support pillars 107 each comprise a region of the dielectric layer 111 whose sides and bottom are coated with a portion of the insulating layer 123. In this case, the support elements of the GMR filter are thus entirely made of one or more dielectric materials. In the bolometric detector 200, the support elements of the GMR filter comprise a single dielectric material.

[0096] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art. In particular, although examples of bolometric detectors 100, 200, 300 and 400 using silicon oxide sacrificial layers have been detailed above, the described embodiments are not limited to this case but apply more generally to any type of bolometer technology. Furthermore, although the description takes as an example bolometric detectors adapted to detect LWIR infrared radiation, this example is not limiting, the embodiments of the present description applying to bolometric detectors capable of detecting infrared radiation in any range.

[0097] Furthermore, although examples of bolometric detectors 100, 200, 300 and 400 comprising a filter for each pixel have been described, the embodiments are not limited to these examples. In particular, certain pixels of the detector may be without a filter, for example in the case of white pixels or broadband pixels. Thus, at least one of the pixels of the detector comprises a guided mode filter comprising a planar waveguide resting on support pillars of a bolometric board and a diffraction grating located on and in contact with the waveguide. The person skilled in the art is capable of manufacturing such a device from the indications of the description above.

[0098] Finally, the practical implementation of the described embodiments and variants is within the reach of those skilled in the art from the functional indications given above. In particular, the described embodiments are not limited to the particular examples of materials and dimensions mentioned in the present description.

Claims

Claims

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

2. Detector (100; 200; 300; 400) according to claim 1, wherein the guided mode filter comprises support elements resting on the support pillars (107).

3. A 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) of claim 2, wherein each support member consists of a single dielectric region (111).

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

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

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

8. A detector (300; 400) according to claim 6 or 7, wherein the second material is alumina.

9. A detector (300; 400) according to claim 6, 7 or 8, wherein at least two adjacent pixels comprise the guided mode filter, the planar waveguides (111) of said pixels being optically isolated by an electrically conductive region (303).

10. A detector (300; 400) according to claim 9, wherein the electrically conductive region (303) and the diffraction grating (113) are in the same material, preferably a metal.

11. Detector (300; 400) according to claim 9, wherein the electrically conductive region (303) and the diffraction grating (113) are made of different materials, preferably metals.

12. A detector (100; 200; 300; 400) according to any one of claims 1 to 11, wherein the diffraction grating (113) comprises a plurality of pads (115) located on and in contact with the upper face of the planar waveguide (111).

13. A method of manufacturing a bolometric detector (100; 200; 300; 400) according to any one of claims 1 to 12, comprising the following steps: a) forming the support pillars (107) and the bolometric boards (101) above the substrate (103); b) depositing a first sacrificial layer (109) on the side of the upper face of the structure; c) forming, for said at least one of said pixels, the planar waveguide (111) and the diffraction grating (113); d) forming vias (121; 201) throughout the thickness of the first dielectric layer (109) directly above each support pillar (107); e) depositing a second insulating layer (123) on the side of the upper face of the structure; and f) depositing an electrically conductive layer (125) on the upper face side of the structure.

14. The method of claim 13, wherein step f) is performed after step e).

15. The method of claim 13, wherein step f) is performed before step c).

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