Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
  • G01J5/10—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors
  • G01J5/20—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/12—Generating the spectrum; Monochromators
  • G01J3/26—Generating the spectrum; Monochromators using multiple reflection, e.g. Fabry-Perot interferometer, variable interference filters
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
  • G01J5/02—Constructional details
  • G01J5/04—Casings
  • G01J5/041—Mountings in enclosures or in a particular environment
  • G01J5/045—Sealings; Vacuum enclosures; Encapsulated packages; Wafer bonding structures; Getter arrangements
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
  • G01J5/02—Constructional details
  • G01J5/08—Optical arrangements
  • G01J5/0801—Means for wavelength selection or discrimination
  • G01J5/0802—Optical filters
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
  • G01J5/02—Constructional details
  • G01J5/08—Optical arrangements
  • G01J5/0875—Windows; Arrangements for fastening thereof
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
  • G01J5/10—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors
  • G01J5/20—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors using resistors, thermistors or semiconductors sensitive to radiation, e.g. photoconductive devices
  • G01J2005/202—Arrays

Definitions

• the invention relates to the field of infrared detection, and in particular detection using micro-bolometers.
• the invention relates to an infrared detector produced using the transfer manufacturing of an optical window on a base substrate.
• the invention aims to limit the deflections likely to appear, during vacuum sealing after this transfer, between the optical window and the base substrate. This limitation of the deflections makes it possible in particular to obtain infrared detectors, produced using the transfer manufacturing, with a large number of pixels and/or with increased precision.
• the invention can be implemented in many fields for which infrared images are currently used, such as the fields of aerospace, security, defense, transportation, thermography, industrial inspection, building inspection, leisure, health, etc.
• an infrared detector 100 is conventionally in the form of a hermetic cavity 16 integrating a network of micro-bolometers 19.
• Each micro-bolometer 19 comprises a membrane 15 mounted in suspension on a base substrate 11 by means of anchoring nails 14.
• the hermetic cavity 16 is generally constituted by an optical window 12 and side walls 13 fixed between the base substrate 11 and the optical window 12.
• a microbolometer 19 is for example designed to exhibit maximum sensitivity over the wavelength range of interest 8-14 micrometers, while being insensitive to flux outside this spectral band. Intrinsically, the uncoated optical window exhibits a transmittance wider than the wavelength range of interest.
• this optical window is treated or structured with respect to the micro-bolometers 19.
• this optical window is intended to attenuate wavelengths between 2 and 8 micrometers, and to form an anti-reflection filter for wavelengths of interest between 8 and 14 micrometers.
• the optical window 12 may comprise a first filter 17 and a second filter 18, formed respectively on the lower face and the upper face of the optical window 12.
• separate filters can be associated with separate microbolometers 19.
• this embodiment requires limiting the distance between the optical window 12 and the microbolometers 19 so that the infrared radiation intended for a specific microbolometer 19 mainly passes through the associated filter.
• the performance of the infrared detector 100 is also related to the vacuum level within the hermetic cavity 16.
• the vacuum level in the hermetic cavity 16 must typically be less than 10' 2 mbar.
• the optical window 12 is vacuum sealed on an upper end of the side walls 13 above the base substrate 11 and the microbolometers 19.
• the invention more specifically targets manufacturing by transfer, detectable on an infrared detector 100 because the optical window does not include a vent.
• the vacuum level can cause a deflection of the optical window 12 and/or the base substrate 11, as illustrated in FIG. 1.
• These deflections reduce the distance Hmin between the optical window 12 and the base substrate 11.
• the optical window 12 can come into contact with the microbolometers 19, or even destroy or degrade them.
• the deflection of the optical window 12 can also lead to a degradation of the filtering properties of the filters 17-18 and disturb the optical signal received by the micro-bolometers 19.
• the deflection depends mainly on the vacuum level in the hermetic cavity 16, on the external pressure, i.e. the pressure of the medium in which the detector is located, on the surface of the infrared detector 100, on the thickness Es and the nature of the base substrate 11, and on the thickness Ef and the nature of the optical window 12.
• the possible surface limits for the infrared detector 100 as a function of the thickness Es and the nature of the base substrate 11 and the thickness Ef and the nature of the optical window 12.
• the deflection phenomenon limits the possibilities of producing an infrared detector 100 for applications in which the distance between the optical window 12 and the microbolometers 19 is small.
• the technical problem that the invention seeks to solve therefore consists in proposing an infrared detector having a large and/or thin substrate and optical window while limiting the deflection.
• the invention proposes to address this technical problem by placing spacers between the upper end of at least part of the anchor nails and the lower surface of the optical window. These spacers form a mechanical stop capable of opposing these deflections of the optical window and/or the base substrate.
• the invention relates to an infrared detector comprising: a base substrate supporting an array of microbolometers, each microbolometer being suspended above said substrate by means of anchoring nails extending substantially perpendicularly relative to the base substrate; side walls extending substantially perpendicularly relative to the base substrate; and an optical window fixed on an upper end of the side walls above the microbolometers, the optical window not comprising a vent; the base substrate, the side walls and the optical window forming a vacuum-sealed cavity within which the microbolometers are present.
• the infrared detector also comprises spacers extending vertically above at least 10% of the anchoring nails, these spacers also being oriented substantially perpendicularly relative to the base substrate, said spacers forming a stop capable of cooperating with the lower face of the optical window, or with the upper end of the anchoring nails, and thus limiting the deflections of the optical window and/or the substrate.
• the invention thus makes it possible, with the manufacturing by transfer, to limit the deflections of the optical window and/or the substrate. With these limited deflections, it is now possible to limit the thickness of the optical window and the base substrate without risking degrading the microbolometers after vacuum sealing of the hermetic cavity. Indeed, the optical window no longer risks coming into contact with the suspended membranes of the microbolometers.
• At least 10% of the anchor nails must be associated with a spacer oriented substantially perpendicular to the base substrate.
• spacers can be distributed evenly across the anchor nails, for example across all anchor nails or every 2, 4 or 8 anchor nails in a row.
• the spacers may also be distributed according to a non-uniform distribution law that increases the number of spacers at the center of the infrared detector.
• This embodiment makes it possible to limit the number of spacers by placing a large number of spacers in the areas most sensitive to deflections, typically the center of the infrared detector.
• the spacers can have a cross section between 0.5 and 1.5 square micrometers. Additionally, the height of the spacers may be at least twice that of the anchor nails, typically a height of 5 micrometers compared to a height of the anchor nails of the order of 2 micrometers.
• the contact between the spacers and the optical window or the anchor nails is observed after vacuum sealing of the cavity.
• the spacers can be previously fixed on the optical window or on the anchor nails.
• the base substrate and the optical window are placed in a vacuum sealing oven. After sealing, the pressure rises in the sealing oven and deflections of the optical window or the base substrate can then appear.
• the spacers are made on the lower face of the optical window and come into contact with the anchoring nails of the base substrate after vacuum sealing of the cavity formed around the micro-bolometers by the base substrate, the side walls and the optical window.
• the spacers are made in the extension of the anchoring nails of the base substrate and come into contact with the optical window after vacuum sealing of the cavity formed around the micro-bolometers by the base substrate, the side walls and the optical window.
• the optical window may be provided with flat areas intended to cooperate with the upper end of the spacers after vacuum sealing of the cavity.
• the optical window can be provided on its upper face with a multilayer interference filter or a periodic diffraction grating, and on its lower face, with a multilayer interference filter or a periodic diffraction grating.
• the lower face is structured by a periodic diffraction grating, it is advantageous to provide flat areas to receive the spacers and limit possible degradation of the patterns of said grating.
• an upper support transparent to radiation in the wavelength range of interest of the microbolometers, can be formed on the spacers.
• the infrared detector includes an upper support attached to the upper end of the spacers and positioned between the spacers and the optical window after vacuum sealing the cavity.
• the wavelength range of interest typically corresponds to the range of 8-14 micrometers.
• the invention can implement known additive manufacturing steps using several sacrificial layers.
• the invention also relates to a method for producing an infrared detector comprising the following steps: depositing and structuring a first sacrificial layer on a base substrate; forming anchoring nails through the first sacrificial layer until reaching the base substrate; forming membranes on the first sacrificial layer and the anchoring nails; depositing and structuring a second sacrificial layer on the membranes and the first sacrificial layer; forming spacers through the second sacrificial layer and in the extension of at least part of the anchoring nails; and removing the sacrificial layers so as to release the microbolometers formed by the membranes and the anchoring nails; producing an optical window; forming side walls on the base substrate or the optical window and around the microbolometers; the side walls being produced before removing the sacrificial layers when they are formed on the base substrate; transfer of the optical window to the base substrate; and vacuum sealing of the cavity formed by the base substrate, the side walls and the optical window; the spacers forming
• Figure 1 illustrates a schematic sectional view of a state-of-the-art infrared detector
• Figure 2 illustrates a schematic sectional view of an infrared detector according to a first embodiment of the invention before the step of vacuum sealing the housing;
• Figure 3 illustrates a schematic sectional view of the infrared detector of Figure 2 after the vacuum sealing step of the housing;
• Figure 4 illustrates a schematic sectional view of an infrared detector according to a second embodiment of the invention before the step of vacuum sealing the housing;
• Figure 5 illustrates a schematic sectional view of the infrared detector of Figure 4 after the vacuum sealing step of the housing;
• Figure 6 illustrates a schematic sectional view of an infrared detector according to a third embodiment of the invention before the step of vacuum sealing the housing;
• Figure 7 illustrates a schematic sectional view of the infrared detector of Figure 6 after the vacuum sealing step of the housing;
• Figure 8 illustrates a schematic sectional view of an infrared detector according to a fourth embodiment of the invention before the step of vacuum sealing the housing;
• Figure 9 illustrates a schematic sectional view of the infrared detector of Figure 8 after the vacuum sealing step of the housing.
• Figures 10 to 16 illustrate a schematic sectional view of the steps in producing a base substrate for the infrared detector of Figure 2.
• each microbolometer 19 comprises a membrane 15 suspended above the base substrate 11 by means of anchoring nails 14.
• each membrane 15 may be mounted on two or four anchoring nails 14 by means of suspension arms intended to limit thermal conduction between the membrane 15 and the base substrate 11.
• the base substrate 11 may also support a reflector arranged under the membranes 15.
• Microbolometers 19 are typically arranged in an array of rows and columns to form the image points, or pixels, of an infrared image.
• microbolometers 19 shown in FIGS. 2 to 9 may also be structured on the base substrate 11, for example microbolometers thermalized with the substrate, in order to reject a non-useful component of the signal, called common mode, which may be largely predominant. The rejection of this component makes it possible to read the useful signal by making maximum use of the electrical dynamics of the reading circuit.
• spacers 20 are formed on several anchor nails 14 of the detection micro-bolometers 19.
• the spacers 20 extend vertically above at least 10% of the anchor nails 14 and substantially perpendicularly relative to the base substrate 11.
• every other microbolometer 19 has spacers 20 fixed to anchor nails 14.
• the distribution of the spacers 20 can take different forms without changing the invention, provided that at least 10% of the anchor nails 14 are surmounted by spacers 20.
• the distribution of the spacers 20 can be uniform.
• These spacers 20 can in particular be placed on all the anchor nails 14, on every other anchor nail 14, on every four anchor nails 14 or even on every eight anchor nails 14, without changing the invention.
• the distribution of the anchor nails 14 may also be non-uniform, i.e., more spacers 20 are placed in certain areas of the infrared detector 10a-10d.
• the boundary between the central area and the peripheral area of the infrared detector 10a-10d may be determined such that the central area covers an area twice as small as the peripheral area, or by any other mathematical definition.
• an infrared detector 10a-10d also includes an optical window 12 attached to an upper end of side walls 13 and above the microbolometers 19.
• the side walls 13 may be formed independently of the base substrate 11 and the optical window 12 and attached to the base substrate 11 before the optical window 12 is attached. Alternatively, it is possible to structure the base substrate 11 or the optical window 12 so as to form side walls 13.
• these side walls 13 can be made of amorphous silicon allowing the micro-bolometers 19 to be encapsulated laterally. Whatever the technology for forming the side walls 13, they extend substantially perpendicularly relative to the base substrate 11 and allow a hermetic vacuum cavity 16 to be formed by fixing the optical window 12 to the upper ends of said walls.
• the spacers 20 form a stop between the anchoring nails 14 of the micro-bolometers 19 and the optical window 12.
• the optical window 12 is structured by filters making it possible to limit the incident radiation on the micro-bolometers 19.
• the optical window 12 is structured with two interference multilayer filters 17 and 18.
• the total thickness Ef of the optical window 12 therefore corresponds to the thickness of the substrate of this optical window 12 added to the thickness of the two interference multilayer filters 17 and 18.
• the spacers 20 do not necessarily touch the optical window 12. After vacuum sealing, necessary to form the infrared detector 10a illustrated in Figure 3, a deflection appears and this deflection causes contact between the spacers 20 and the optical window 12. More precisely, in the example of Figure 3, the spacers 20 come into contact with the interference multilayer filter 17 produced on the lower face of the optical window 12.
• the height of the anchoring nails 14 and the spacers 20 makes it possible to define the minimum height Hmin of the cavity 16. Indeed, when the optical window 12 comes into contact with the spacers 20, the deflections of the optical window 12 and/or the base substrate 11 are limited.
• the height of the anchoring nails 14 can be between 2 and 2.5 micrometers while the height of the spacers 20 can be between 5 and 10 micrometers.
• the spacers 20 preferably have a smaller section than the anchoring nails 14.
• the anchoring nails 14 may have a section of 2 square micrometers while the spacers 20 may have a cross section of between 0.5 and 1.5 square micrometers.
• the anchoring nails 14 conventionally integrate metal elements making it possible to reestablish contact with the membrane 15.
• these metal elements are naturally thermal conductors.
• the spacers 20 they have no electrical conduction function so that they can be made of a thermally insulating material, such as amorphous silicon.
• the optical window 12 has a periodic diffraction grating 21 structured on its lower face.
• This periodic diffraction grating makes it possible, like the interference multilayer filters, to filter part of the incident infrared radiation.
• a periodic diffraction grating is more sensitive to the risks of deterioration due to contact with a spacer 20.
• spacers 20 whose section is approximately 1 square micrometer, and an alignment precision of the optical window 12 relative to the base substrate 11 of the order of 2 micrometers when transferring the optical window 12, flat areas of between 3 and 5 micrometers on each side can be produced.
• the spacers 20 come into contact with the flat areas 22 of the optical window 12 after vacuum sealing of the cavity 16, so as to limit the possible deterioration of the periodic diffraction gratings 21.
• an upper support 23 transparent to infrared radiation in the wavelength range of interest of the microbolometers 19, is placed above the spacers 20.
• This upper support 23 makes it possible to constitute a support zone for the optical window 12 in order to distribute the mechanical pressure of supporting the spacers 20 with the optical window 12. In doing so, the risk of deterioration of a periodic diffraction grating 21 formed on the lower face of the optical window 12 is limited, and it is no longer necessary to provide flat areas.
• this upper support extends over the entire surface of the microbolometers 19 in the example of FIGS. 6 and 7.
• this upper support 23 may extend only to the center of the infrared detector 10c.
• spacers 20 are fixed on the lower face of the optical window 12 and come into contact with the anchoring nails 14 after vacuum sealing of the cavity 16.
• This embodiment also makes it possible to guarantee a minimum height Hmin between the optical window 12 and the base substrate 11.
• Figures 10 to 16 illustrate an embodiment of spacers 20 on the anchor nails 14 of a base substrate 11.
• a first step consists of depositing and structuring a sacrificial layer 30 on a base substrate 11.
• the anchoring nails 14 are then formed during a second step inside the structuring patterns of the sacrificial layer, as illustrated in FIG. 11.
• the membranes 15 of the different micro-bolometers 19 are then formed on the sacrificial layer 30 and the anchoring nails 14, as illustrated in FIG. 12.
• a second sacrificial layer 31 is deposited on the membranes 15 and on the first sacrificial layer 30.
• This second sacrificial layer 31 is also structured in order to define areas for which the spacers 20 are to be produced, and in this case, in the extension of the anchor nails 14, as illustrated in FIG. 13.
• the spacers 20 can then be formed by deposition of material in the structuring patterns of the second sacrificial layer 31.
• This deposition can consist of amorphous silicon produced by physical vapor deposition.
• the thin layer of amorphous silicon 43 deposited on the second sacrificial layer 31 can then be removed, for example by reactive ion etching, as illustrated in FIG. 15.
• the optical window 12 To obtain an infrared detector, it is also appropriate to produce the optical window 12, to form the side walls 13 on the base substrate 11 or on the optical window 12, to transfer the optical window 12 onto the base substrate 11 and to vacuum seal the optical window 12 onto the base substrate 11 in order to form the cavity 16.
• the side walls 13 are formed on the base substrate 11, these are conventionally formed before the release of the micro-bolometers 19.
• the invention makes it possible to obtain a cavity 16 with a fixed minimum height Hmin between the base substrate 11 and the optical window 12 so that it is possible to use a base substrate 11 with a thickness Es less than the thicknesses of the prior art or even an optical window 12 with a thickness Es less than the thicknesses of the prior art while overcoming the constraints of bringing these two elements together. It is also possible to form infrared detectors 10a-10d with detection surfaces greater than the surfaces of the prior art.
• the invention makes it possible to obtain an infrared detector having a substrate and an optical window of large size and/or fine.
• the invention makes it possible, for example, to produce an infrared detector with separate filters for different microbolometers or, more simply, to limit the distance between the optical window 12 and the microbolometers 19 to simplify the manufacturing process or limit the size.

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• Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• General Physics & Mathematics (AREA)
• Photometry And Measurement Of Optical Pulse Characteristics (AREA)

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• 2023
  • 2023-02-06 FR FR2301102A patent/FR3145611B1/fr active Active
  • 2023-12-13 EP EP23837743.6A patent/EP4662466A1/de active Pending
  • 2023-12-13 KR KR1020257025458A patent/KR20250142864A/ko active Pending
  • 2023-12-13 CN CN202380089215.2A patent/CN120390869A/zh active Pending
  • 2023-12-13 WO PCT/FR2023/051993 patent/WO2024165799A1/fr not_active Ceased

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