MICRO-BOLOMETRE FOR BLIND INFRARED IMAGING AND PROCESS FOR IMPLEMENTATION

Abstract

The invention relates to a blind infrared imaging microbolometer (10) comprising: – a substrate (11); – a membrane (14); and – a blocking screen (19) disposed above the membrane (14) so ​​as to block incident infrared radiation; said blocking screen (19) comprising: at least one metallic layer having a thickness greater than 150 nanometers; and at least two release vents (32) for allowing the removal of at least one sacrificial layer implemented during the manufacturing process of the blind microbolometer (10), each release vent (32) having an opening ratio of less than 30% and a size of less than 3 micrometers. Figure for abbreviation: Fig 1

Description

Title of the invention: MICRO-BOLOMETRE FOR BLINDING INFRARED IMAGING AND METHOD FOR IMPLEMENTATION Scope of the invention

[0001] The present invention relates to the field of electromagnetic radiation detection and, more specifically, to the compensation of detection errors of infrared detectors implementing micro-bolometers.

[0002] The invention relates, on the one hand, to a blind micro-bolometer and, on the other hand, to an associated method of embodiment. Prior state of the art

[0003] In the field of detectors used for infrared imaging, it is known to use devices arranged in matrix form, capable of operating at room temperature, i.e. not requiring cooling at very low temperatures, unlike detection devices called "quantum detectors" which require operation at very low temperature.

[0004] These detectors traditionally use the variation of a physical quantity of a suitable material or assembly of materials as a function of temperature, in the vicinity of 300K.

[0005] In the particular case of micro-bolometric detectors, the most commonly used, this physical quantity is the electrical resistivity, but other quantities can be exploited, such as the dielectric constant, the polarization, the thermal expansion, the refractive index, etc.

[0006] Such an uncooled detector generally combines: - means of absorbing thermal radiation and converting it into heat; - means of thermally insulating the detector, so as to allow it to heat up under the action of thermal radiation; - thermometry means which, within the framework of a micro-bolometric detector, implement a resistive element whose resistance varies with temperature; - and means of reading the electrical signals provided by the thermometry means.

[0007] Detectors for thermal, or infrared, imaging are typically made in the form of an array of elementary detectors, forming image points or pixels, in one or two dimensions. To ensure thermal insulation of the detectors, they are suspended above a substrate by means of support arms. The absorption and thermometry means are then combined. to form a membrane mounted in suspension above the substrate by means of pads on which the support arms are fixed.

[0008] The substrate usually includes means for sequentially addressing the elementary detectors and means for electrically exciting and pre-processing the electrical signals generated from these elementary detectors. This substrate and the integrated means are commonly referred to as the "reading circuit".

[0009] In the case of infrared detectors using microbolometers, the pre-processing means may incorporate microbolometers dedicated to compensating for undesirable effects that degrade the quality of the measured signals. These microbolometers dedicated to compensation are called reference microbolometers. A differential measurement is then generally performed between a sensitive microbolometer and a reference microbolometer to filter each measurement from a sensitive microbolometer.

[0010] For example, some reference microbolometers allow the rejection of a non-useful component of the signal, called the common mode, which can be largely predominant. Rejecting this component allows the useful signal to be read by making maximum use of the electrical dynamics of the readout circuit. To achieve this, these reference microbolometers are thermally bonded to the substrate and lack an absorbing layer.

[0011] The invention relates more specifically to another type of reference microbolometers; so-called blind reference microbolometers, which allow, in association with detection microbolometers, the differential measurement of a temperature variation by means of a thermometric material present in both the detection microbolometers and the blind microbolometers.

[0012] Thus, unlike reference microbolometers thermalized with the substrate, blind reference microbolometers are not thermalized with the substrate and are equipped with an occultation screen.

[0013] The temperature variation detected by the thermometric material results from several factors: the useful flux to be detected, the self-heating inherent in the reading mode, and parasitic fluxes. In order to improve measurement accuracy, the screening of the blind microbolometers aims to effectively compensate for any source of temperature variation other than that arising from the useful flux to be detected, between the detection microbolometers and the compensation microbolometers.

[0014] According to this approach, these two types of micro-bolometers preferentially have the same thermal and electrical properties so as to guarantee the accuracy of the measurement.

[0015] In the case of blind microbolometers, the formation of the occultation screen on the membrane greatly complicates the removal of the sacrificial layers placed in The process involves creating a suspended membrane and then forming the blackout screen on top of it. The blackout screen must be suspended above the membrane. This is achieved by using a second sacrificial layer placed on top of the membrane and on top of the first sacrificial layer surrounding it. Openings are made in this second sacrificial layer around the membrane to allow for the placement of a supporting structure before the blackout screen is formed on top of this supporting structure.

[0016] To eliminate the second sacrificial layer, and potentially the first sacrificial layer simultaneously, it is necessary to provide at least one release vent in the occultation screen or within the supporting structure. Generally, the occultation screen or the supporting structure is shared by several blind microbolometers arranged at the base of a row or column, and a vent is provided for each blind microbolometer.

[0017] The release of the microbolometer membrane, i.e., the removal of the sacrificial layers, is then carried out by removing the sacrificial layers through the release vents. Conventionally, the release process uses oxygenated plasma etching to remove sacrificial layers typically made of polyimide.

[0018] Thus, as described in document JP 2011 / 232157, the release vents are used so that the flows of reactive gases and reaction products enter and exit the cavity formed by the blackout screen and the supporting structure perpendicular to the plane formed by the blackout screen.

[0019] However, the implementation of the release vents within the occultation screen poses a technical problem.

[0020] Indeed, some of the infrared radiation can pass through these vents and cause unwanted heating of the membrane. As a result, the microbolometer's blinding is not perfect, and the compensation is not always effective, thus degrading the overall image from the infrared sensor.

[0021] To resolve this technical problem, one solution is to form the release vents in an area of ​​the blackout screen that is not located opposite the membrane. To this end, document EP 3 243 052 proposes a load-bearing structure in the form of steps, that is to say, with at least one intermediate step between the plane of the substrate and the plane of the blackout screen. Thus, the load-bearing structure has a step plane parallel to the planes of the substrate, the membrane, and the blackout screen, respectively, and this parallel step plane can be used to position the release vents.

[0022] This solution, consisting of relocating the release vents to a horizontal surface of an intermediate step of a stepped structure, allows This effectively limits the degradation of the occulting screen's optical properties inherent to the presence of release vents, as these vents can be positioned at the same level as the membrane plane, thus limiting the propagation of stray radiation that could pass through the vents to reach the membrane. However, this solution requires enlarging the support structure to accommodate the release vents, thereby limiting the integration density of these blind microbolometers.

[0023] Furthermore, to effectively limit the propagation of stray radiation that could pass through the release vents and consequently reach the membrane, it is conventionally necessary to limit the cross-section of the release vents, even when using vents located on an intermediate step of a stepped support structure. For example, EP 2 633 279 proposes using a release vent for each blind microbolometer with a size less than 1 micrometer in order to effectively attenuate the transmission of infrared radiation through the release vent.

[0024] Within the scope of the invention, it has been determined numerically that, for a square-section release vent located above a bolometric membrane, the length limit on each side of the vent is 1.6 micrometers to obtain acceptable parasitic radiation, i.e., a screening power of at least 99%. The cross-section of the release vent in this simulation is therefore 2.56 pm².

[0025] For the purposes of this invention, the "screening power" corresponds to the percentage of incident flux blocked by the occulting screen. The electro-optical response of a microbolometer, also called the residual response, is the difference in DC level measured when this microbolometer is successively illuminated by two black bodies at different temperatures. This residual response is therefore expressed in V / K or, more commonly, in mV / K.

[0026] To evaluate the screening power, it is possible to measure the residual response of a blind microbolometer and that of a detection microbolometer located near the blind microbolometer. The screening power then corresponds to the ratio between the two responses, i.e., the response of the detection microbolometer minus the response of the blind microbolometer divided by the response of the detection microbolometer. Preferably, the response values ​​are obtained by averaging over a set of detection and blind microbolometers.

[0027] Due to the limited dimensions of the release vents, the release rate, i.e., the time required to remove the entire volume of the sacrificial layers through said vents, is particularly long. For example, the release rate of a membrane through the vents can be on the order of one hour, whereas the membranes of the detection microbolometers, i.e. the Membranes not covered by the blackout screens can be released in 15 minutes.

[0028] This difference in the release times of the membranes can lead to over-etching of the membranes of the detection microbolometers compared to the membranes of the compensation microbolometers.

[0029] Although the membranes of the compensation microbolometers and the detection microbolometers are preferably made simultaneously to have the same thermal and electrical properties, this over-etching of the membranes of the detection microbolometers can lead to discrepancies between the thermal and electrical properties of the detection microbolometers and the compensation microbolometers.

[0030] Thus, this over-etching can degrade the accuracy of the compensation performed by the compensation micro-bolometers.

[0031] More specifically, a relative difference between the resistances of blind microbolometers and those of detection microbolometers of less than 1% is sought.

[0032] For the purposes of this invention, the "relative difference" corresponds to the percentage difference in resistance between a blind microbolometer and a detection microbolometer located near the blind microbolometer. This resistance can be easily measured across the terminals of the blind microbolometer and the terminals of the detection microbolometer in a dark chamber, i.e., without infrared radiation being detected by the detection microbolometer. The relative difference therefore corresponds to the ratio between the two resistance measurements, namely the resistance measurement of the detection microbolometer minus the resistance measurement of the blind microbolometer divided by the resistance measurement of the detection microbolometer. Preferably, the measurements are averaged over a set of detection and blind microbolometers.

[0033] The technical problem that the invention aims to solve therefore consists of obtaining a blind infrared imaging microbolometer having release vents that limit parasitic radiation and allow for an acceptable release velocity of the blind microbolometer membrane, close to that of the membranes of detection microbolometers, while limiting the difference between the resistance of a blind microbolometer and that of a detection microbolometer. Description of the invention

[0034] In order to address this technical problem, the invention proposes to use at least two blind microbolometer release vents with sufficiently small dimensions to limit the transmission of infrared radiation.

[0035] Indeed, the invention stems from the observation that increasing the number of small release vents does not increase the transmittance of infrared radiation through the shading screen. Because of this counterintuitive observation, a person skilled in the art, who would naturally have assumed that the transmittance of infrared radiation is directly proportional to the open area of ​​the shading screen, also known as the openness ratio, would not have pursued this approach.

[0036] In the sense of the invention, the "opening rate" of the blackout screen thus corresponds to the total surface area of ​​the release vents formed opposite a blind microbolometer on the total surface area of ​​the blind microbolometer.

[0037] For reasons of simplification of the manufacturing process, the prior art always proposes to use a single release vent when it is arranged opposite the blind microbolometer.

[0038] Based on the observation of the invention that these two constraints are not inextricably linked, it is now possible to limit the release time of the membrane of the blind microbolometer without degrading the transmittance of infrared radiation through the occultation screen by multiplying the vents through said screen.

[0039] To obtain this surprising effect, it has been observed that it is necessary to use an occultation screen with a sufficiently thick metallic layer, typically a metallic layer with a thickness greater than 150 nanometers.

[0040] Furthermore, each release vent must have an opening rate of less than 30% and a size of less than 3 micrometers.

[0041] For the purposes of the invention, the "size" of a release vent corresponds to the largest dimension of said vent, for example the diagonal of a square or rectangular vent or the diameter of a circular vent.

[0042] According to a first aspect, the invention relates to a blind infrared imaging microbolometer comprising: - a substrate; - a membrane, comprising at least two electrodes and a thermo-resistive element, mounted in suspension above the substrate; - a blackout screen positioned above the membrane so as to block incident infrared radiation; said blackout screen being suspended above the membrane and the substrate by means of a support structure fixed to the substrate; and - a release vent provided within said occultation screen and intended to allow the removal of at least one sacrificial layer implemented during the manufacturing process of the blind microbolometer.

[0043] The invention is characterized in that the blackout screen comprises: - at least one metallic layer with a thickness greater than 150 nanometers; and - at least two release vents, each release vent having an opening rate of less than 30% and a size of less than 3 micrometers.

[0044] The invention makes it possible to obtain a blind microbolometer, or a set of blind microbolometers made collectively, with a screening power of at least 99% and a relative difference between the resistances of the blind microbolometers and that of the detection microbolometers of less than 1%.

[0045] This improvement in the relative difference is inherent in the reduction of the release time because the exposure time of the membranes of the detection microbolometers is now closer to the exposure time of the membranes of the blind microbolometers, and the risk of over-etching of the membranes of the detection microbolometers is limited.

[0046] This reduction in release time depends on the opening ratio of the shading screen. The possible increase in this opening ratio to maintain a shading capacity of at least 99% depends on the initial shading capacity of the shading screen, that is, on the nature and thickness of the metallic layer integrated into said screen. Of course, it is possible to implement the invention to obtain a shading capacity lower than 99%.

[0047] For example, for an occultation screen comprising a metallic layer made of titanium or chromium, the thickness of the metallic layer is preferably greater than 400 nanometers and the opening ratio is preferably less than 25%.

[0048] In another example in which the occulting screen comprises a metallic layer made of aluminium, gold, silver, copper, platinum, molybdenum or tungsten, the thickness of the metallic layer is preferably greater than 100 nanometres and the opening ratio is preferably less than 25%.

[0049] Thus, the variation in the possible opening rate depends on the thickness and nature of the metallic layer constituting the occultation screen.

[0050] Furthermore, the opening rate can be obtained with release vents of varying shapes without changing the invention.

[0051] For example, the release vents can be square, rectangular, circular, hexagonal...

[0052] It is nevertheless important that the size of each vent be less than 3 micrometers.

[0053] The vents can be placed randomly in the occultation screen or arranged in the form of a periodic network of at least four micro-release vents blind bolometer, the release vents being arranged for example in rows and columns.

[0054] For the purposes of this invention, a "periodic array" indicates that the vents of each blind microbolometer are regularly spaced from one another by a regular pitch. With at least two rows and two columns, the periodic array is formed with a minimum of four release vents. Of course, it is possible to use more than two columns or more than two rows.

[0055] For example, for a periodic array of three rows and three columns, while the maximum cross-section of a single release vent was previously estimated at 2.56 pm² to obtain a screening power greater than 99%, it has been observed that it is possible to use a periodic array of 9 circular release vents with a diameter of 1.4 micrometers and a pitch of 4 micrometers between the vents and also obtain a screening power greater than 99%. With this particular configuration, the cross-section of each release vent is 1.54 pm² and the total cross-section is 13.85 pm². Since the release velocity is directly related to the total cross-section of the release vents of each blind microbolometer, increasing the cross-section from 2.56 pm² to a total cross-section of 13.85 pm² significantly improves the release velocity.It is therefore possible to obtain a relative difference between the resistances of blind microbolometers and those of detection microbolometers of less than 1%.

[0056] Simulations of the invention have shown that the invention is particularly effective with networks of nine or sixteen release vents, with three rows and three columns or with four rows and four columns.

[0057] According to a second aspect, the invention relates to a method for manufacturing a blind infrared imaging microbolometer comprising the following steps: - making the membrane on a first sacrificial layer deposited on a substrate; - deposition of a second sacrificial layer on the membrane and on the first sacrificial layer; - making openings at the periphery of the membrane within said first and second sacrificial layers until reaching the substrate; - deposition of at least one blinding layer on the second sacrificial layer and in the openings, so as to form an occultation screen and a load-bearing structure; said at least one blinding layer comprising at least one metallic layer having a thickness greater than 150 nanometers; - implementation of at least two release vents in the occultation screen, each release vent having an opening rate of less than 30% and a size of less than 3 micrometers; and - removal of the first and second sacrificial layers by means of an etching fluid through the release vents thus formed.

[0058] The use of several release vents with an opening rate of less than 30% and a size of less than 3 micrometers makes it possible to limit the release time of the membrane of the blind microbolometer. Thus, the step of removing the first and second sacrificial layers is preferably carried out in a time of less than 10 minutes. Brief description of the figures

[0059] The invention will be better understood upon reading the following description, the details of which are given solely by way of example, and developed in relation to the accompanying figures, in which identical references refer to identical elements:

[0060] [Fig-1] is a schematic cross-sectional view of a blind microbolometer according to a embodiment of the invention.

[0061] [Fig.2] is a schematic top view of the blind microbolometer of [Fig.1].

[0062] [Fig.3] is a schematic sectional view of a first stage in the realization of the blind microbolometer of the [Fig.l],

[0063] [Fig.4] is a schematic sectional view of a second stage of realization of the blind micro-bolometer of [Fig.1],

[0064] [Fig.5] is a schematic sectional view of a third stage in the realization of the blind micro-bolometer of [Fig.1],

[0065] [Fig.6] is a schematic sectional view of a fourth stage in the realization of the blind microbolometer of [Fig.1],

[0066] [Fig.7] is a schematic sectional view of a fifth step in the realization of the blind microbolometer of [Fig.1],

[0067] [Fig.8] is a schematic sectional view of a sixth step in the embodiment of the blind microbolometer of [Fig.1], Detailed description of the invention

[0068] Figures 1 and 2 illustrate a blind microbolometer 10 comprising a membrane 14 mounted in suspension on a substrate 11 by anchoring nails 15. The membrane 14 includes a thermo-resistive element and at least two electrodes connected to the anchoring nails 15 to measure the resistance of the thermo-resistive material which varies as a function of its temperature.

[0069] To block infrared radiation that can reach the membrane 14, an occultation screen 19 is fixed above the membrane 14. More specifically, the occultation screen 19 is in the form of a plate supported by a carrier structure 30 fixed to the substrate 11 at the periphery of the membrane 14.

[0070] In the example of Figures 1 and 2, the supporting structure 30 has feet 20 extending from the occultation screen 19 to the substrate 11 by means of two V-shaped side walls 31. Alternatively, the supporting structure 30 can rest on pads placed on the substrate 11.

[0071] According to the invention, the blackout screen 19 comprises at least two release vents 32 having an opening ratio of less than 30% and a size of less than 3 micrometers. As illustrated in [Fig. 2], the release vents 32 may be square and arranged in rows and columns to form a periodic array of sixteen release vents 32. Alternatively, the release vents 32 may have other shapes, for example, a rectangular, circular, or hexagonal shape.

[0072] It is also possible to form a network of 4 or 9 release vents 32 or even to make several distinct release vents 32 without changing the invention.

[0073] In addition, to ensure effective screening of infrared radiation with the multiple release vents 32, the blackout screen 19 must incorporate at least one metallic layer with a thickness greater than 150 nanometers.

[0074] This metallic layer can be the sole constituent layer of the shading screen 19, also used to form the side walls 31 of the supporting structure 30. Alternatively, the metallic layer can be deposited on a support layer or interposed between two encapsulation layers. Thus, the supporting structure 30 may or may not incorporate the metallic layer constituting the shading screen 19.

[0075] The thickness of the metallic layer depends on the material used. For a metallic layer made of titanium or chromium, the thickness of the metallic layer is preferably greater than 400 nanometers and the openness is less than 25%. For a metallic layer made of aluminum, gold, silver, copper, platinum, molybdenum, or tungsten, the thickness of the metallic layer is preferably greater than 100 nanometers and the openness is less than 25%.

[0076] The invention will be better understood with reference to figures 3 to 8 which illustrate the method of making the blind micro-bolometer 10 of figures 1 and 2.

[0077] As illustrated in [Fig.3], a first sacrificial layer 12 is deposited on the substrate 11 so as to allow the formation of the membrane 14. The substrate 11 integrates the addressing and reading elements of the micro-bolometer 10.

[0078] Layers can also be deposited on the substrate 11 before the deposition of this sacrificial layer 12, for example a reflector or a stop layer intended to protect the reading circuit during the step of removing the sacrificial layer 12, for example a layer made of silicon dioxide SiO2.

[0079] Openings 13 are then etched into the first sacrificial layer 12 by reactive ion etching. Reactive ion etching is better known by the acronym RIE for "Reactive-Ion Etching" in the English-language literature.

[0080] Then, as illustrated in [Fig.4], the layers forming the membrane 14, the anchor nails 15, and the support arms of the membrane 14 are then deposited in the openings 13 and on the first sacrificial layer 12.

[0081] For example, the openings 13 can be filled with a conductive material forming the anchor nails 15, such as titanium nitride, or tungsten.

[0082] Conventionally, the elements 14 and 15 incorporate at least metallic layers and support layers so as to form at least two electrodes connected between the substrate 11 and the membrane 14. For example, the electrodes can be made of titanium nitride with a thickness between 5 and 20 nanometers. The support layers can be made of amorphous silicon with a thickness between 10 and 100 nanometers. The membrane 14 also includes a thermoresistive element connected between the two electrodes. This thermoresistive element can be made of amorphous silicon, titanium oxide, or vanadium oxide and deposited by ion beam with a thickness between 10 and 200 nanometers.

[0083] Preferably, the fabrication steps for these elements 14 and 15 of the microbolometer 10 are carried out simultaneously with those of the detection microbolometers (not shown), so that the blind microbolometer 10 formed on the first sacrificial layer 12 has thermal and resistive properties identical to those of the detection microbolometers. For example, the fabrication steps for the microbolometer 10 may correspond to those described in document FR 3045148.

[0084] After delineation and structuring of the membrane 14 and the support arms by one or more reactive ion etchings, a second sacrificial layer 17 is deposited on the first sacrificial layer 12, on the membrane 14 and on the support arms, as illustrated in [Fig. 5]. This second sacrificial layer 17 is preferably made of silicon dioxide SiO2.

[0085] This second sacrificial layer 17 is intended to allow the formation of the support structure 30 and the occulting screen 19, the function of which is to mask the membrane 14 so as to make it very insensitive, or even insensitive, to incident infrared radiation. To achieve this, openings 18 are etched into the two sacrificial layers 12 and 17 by one or more reactive ion etchings until the substrate 11 is reached, as illustrated in [Fig. 6].

[0086] In addition, the sacrificial layers 12 and 17 can conventionally be made of polyimide.

[0087] Preferably, the sacrificial layers 12 and 17 are made of silicon oxide deposited at low temperature, i.e. at a temperature below 400°C by Chemical vapor deposition. Sacrificial layers 12 and 17 made of silicon oxide enable a particularly precise etching process, for example, reactive ion etching with a pitch of less than 1 micrometer. This etching process makes it possible to obtain feet 20 with very thin widths.

[0088] After the discontinuous openings 18 have been made, [Fig.7] illustrates the fabrication of the support structure 30 and the occultation screen 19. To do this, a layer of titanium can be deposited on the second sacrificial layer 17 and in the openings 18 so as to form lateral walls 31 of the support structure 30, as well as the occultation screen 19. This layer of titanium can be deposited by chemical vapor deposition with a thickness of between 400 and 600 nanometers.

[0089] The step illustrated in [Fig. 8] aims to form the release vents 32 and to remove the occultation screen 19 from the expected area covered by the blind microbolometer on the substrate 11, i.e., to prevent the occultation screen 19 from extending into view of the membrane of a neighboring detection microbolometer. This step preferentially defines an overhang 22 on the edges of the openings 18.

[0090] With regard to the release vents 32, this step allows the position, number and shape of the release vents 32 to be defined. Preferably, this step is carried out by a reactive ion etching of the occultation screen 19.

[0091] For example, it is possible to form a periodic array of 16 square-shaped release vents 32 with sides of 1 micrometer and a pitch of 4 micrometers between said vents 32 and obtain a screening power greater than 99%. With this particular configuration, the cross-section of each release vent 32 is 1 pm2 and the total cross-section is 16 pm2.

[0092] Alternatively, it is possible to form a periodic array of 9 circular release vents 32 with a diameter of 1.4 micrometers and a pitch of 4 micrometers between said vents 32 and also obtain a screening power greater than 99%. With this particular configuration, the cross-section of each release vent 32 is 1.54 pm2 and the total cross-section is 13.85 pm2.

[0093] Based on the structure illustrated in [Fig. 8], it is possible to remove the sacrificial layers 12 and 17 using the release vents 32. Thus, the etching fluid is introduced and extracted along with the sacrificial layers 12 and 17 through all of these release vents 32 simultaneously. With the total cross-section of all the release vents 32, the removal of the sacrificial layers 12 and 17 can be carried out in less than 10 minutes.

[0094] Typically, the etching fluid can consist of hydrofluoric acid, allowing the removal of sacrificial layers made of silicon oxide, or even an oxygenated plasma allowing the removal of sacrificial layers made of polyimide.

[0095] Removing the sacrificial layers 12 and 17 allows us to obtain the micro-bolometer 10 illustrated in figures 1 and 2.

[0096] In the example of Figures 1 and 2, the occultation screen 19 covers a single blind microbolometer 10. Alternatively, an occultation screen 19 can cover several blind microbolometers 10 juxtaposed with a single carrier structure 30 common to these different blind microbolometers 10.

[0097] Regardless of the number of blind microbolometers 10 covered by the occultation screen 19, each blind microbolometer 10 is arranged opposite at least two release vents 32 formed in the occultation screen 19 so as to obtain rapid removal of the sacrificial layers 12 and 17.

[0098] The invention thus makes it possible to obtain a blind infrared imaging microbolometer comprising release vents limiting parasitic radiation and allowing to achieve an acceptable release velocity close to that of the membranes of the detection microbolometers, without limiting the integration density of the blind microbolometer.

Claims

Claims

1. Blind infrared imaging micro-bolometer (10) comprising: - a substrate (11); - a membrane (14), comprising at least two electrodes and a thermo-resistive element, mounted in suspension above the substrate (11); and - an occulting screen (19) arranged above the membrane (14) so ​​as to block incident infrared radiation; said occulting screen (19) being mounted in suspension above the membrane (14) and the substrate (11) by means of a supporting structure (20) fixed to the substrate (11); characterized in that said occulting screen (19) comprises: - at least one metal layer having a thickness greater than 150 nanometers;and - at least two release vents (32) provided within said occultation screen (19) opposite said membrane (14) and intended to allow the removal of at least one sacrificial layer (12, 17) implemented during the manufacturing process of the blind micro-bolometer (10), each release vent (32) having a size less than 3 micrometers, so that said occultation screen (19) has an opening rate of less than 30%, the opening rate being defined by the total surface area of ​​said at least two release vents (32) on the total surface area of ​​said blind infrared imaging micro-bolometer (10).;

2. The infrared imaging blind micro-bolometer of claim 1, wherein the occulting screen (19) comprises a metal layer made of titanium or chromium, the thickness of the metal layer being greater than 400 nanometers and the aperture rate being less than 25%.

3. The infrared imaging blind micro-bolometer of claim 1, wherein the occulting screen (19) comprises a metal layer made of aluminum, gold, silver, copper, platinum, molybdenum or tungsten, the thickness of the metal layer being greater than 150 nanometers and the aperture ratio being less than 25%.

4. A blind infrared imaging micro-bolometer according to one of claims 1 to 3, wherein the release vents (32) are organized as a periodic array of at least four release vents (32) per blind microbolometer (10), the release vents (32) being arranged in rows and columns.

5. The infrared imaging blind micro-bolometer of claim 4, wherein the release vents (32) are arranged as a periodic array of nine release vents (32) per blind micro-bolometer (10), with three rows and three columns.

6. The infrared imaging blind micro-bolometer of claim 4, wherein the release vents (32) are arranged as a periodic array of sixteen release vents (32) per blind micro-bolometer (10), with four rows and four columns.

7. A method for producing a blind infrared imaging micro-bolometer (10) comprising the following steps: - producing a membrane comprising at least two electrodes and a thermo-resistive element on a first sacrificial layer (12) deposited on a substrate (11); - depositing a second sacrificial layer (17) on the membrane (14) and on the first sacrificial layer (12); - producing openings (18) at the periphery of the membrane (14) within said first and second sacrificial layers (12, 17) until reaching the substrate (11); - depositing at least one blinding layer on the second sacrificial layer (17) and in the openings (18), so as to form an occultation screen (19) and a supporting structure (20); said at least one blinding layer comprising at least one metal layer having a thickness greater than 150 nanometers;- producing at least two release vents (32) in the occultation screen (19), each release vent (32) having a size less than 3 micrometers so that said occultation screen (19) has an opening rate less than 30%, the opening rate being defined by the total surface area of ​​said at least two release vents (32) over the total surface area of ​​said blind infrared imaging micro-bolometer (10); and - removing the first and second sacrificial layers (12, 17) by means of an etching fluid through the release vents (32) thus formed.;

8. A method of manufacturing a blind infrared imaging micro-bolometer according to claim 7, wherein the metal layer forming part of the occultation screen is made of titanium or chromium, the thickness of said metal layer being greater than 400 nanometers and the opening rate is less than 25%.

9. A method of manufacturing a blind infrared imaging micro-bolometer according to claim 7, wherein the metal layer forming part of the occultation screen is made of aluminum, gold, silver, copper, platinum, molybdenum or tungsten, the thickness of the metal layer being greater than 150 nanometers and the opening rate is less than 25%.

10. A method of manufacturing a blind infrared imaging micro-bolometer according to one of claims 7 to 9, wherein the step of removing the first and second sacrificial layers (12, 17) is carried out for a period of less than 10 minutes.

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