Method for manufacturing an enclosure for a photoacoustic detection device

Abstract

A method for manufacturing an enclosure (2) defining a cavity (4), the enclosure being intended to be applied against a sample to be analyzed (E), the cavity being configured to extend between the sample and an acoustic transducer (T), the cavity opening onto a contact face (3) intended to be applied against the sample, the enclosure comprising: a contact opening (3o), formed in the contact face, opening into the cavity; a membrane (5) extending through the cavity, opposite the contact face, such that all or part of the cavity extends between the membrane and a cover (2c); the method comprising the steps of microstructuring three substrates, so as to form the cover, the rear part of the cavity, the membrane, and the front part of the cavity. Figure 5D

Description

Title of the invention: Method for manufacturing an enclosure for a photoacoustic detection device technical field

[0001] The technical field of the invention is the fabrication of a device for detecting an analyte by photoacoustic effect. The fabrication is carried out by collective microfabrication steps on substrates implemented in the field of microelectronics. EARLIER ART

[0002] Photoacoustic detection is based on the detection of an acoustic wave generated by the absorption, by an analyzed medium, of an incident pulsed or amplitude-modulated electromagnetic wave. The acoustic wave is formed following the heating of molecules of interest present in the analyzed medium, due to the absorption of the incident background radiation. This heating causes a modulated thermal expansion of the medium, which in turn generates the acoustic background radiation.

[0003] Photoacoustic detection can be specific to a particular analyte by adjusting the incident electromagnetic background wavelength to an absorption wavelength of the analyte. Photoacoustic detection has thus been applied to detect gaseous species in a gas, or to detect the presence of particular molecules in biological tissues. The incident background wavelength is frequently in the infrared.

[0004] Photoacoustic detection then constitutes a non-invasive analysis technique, which can be implemented in diffusing or opaque media.

[0005] US patent 11774347 describes a photoacoustic detection device comprising a housing for application against a sample to be analyzed. The housing delimits a cavity opening onto a contact face, the latter being configured to be in contact with the sample. The device includes a membrane extending into the housing, designed to retain moisture and transmit a photoacoustic wave emitted by the sample.

[0006] US patent 11674931 describes a photoacoustic detection device comprising an enclosure for application against a sample to be analyzed. The enclosure defines a cavity opening onto a contact face, the latter being configured to be in contact with the sample. The device includes a tube extending from the cavity to the outside of the cavity. The tube forms a vent of the device. The dimensions of the tube are adapted to the volume of the cavity, in order to optimize the performance of the device.

[0007] The inventors propose a method for manufacturing a device with characteristics as described in US11774347 and / or US11674931, by implementing collective microfabrication processes. The method described below makes it possible to easily produce a photoacoustic detection device, taking advantage of the ability of microelectronics to simultaneously produce a large number of devices. Description of the invention

[0008] A first object of the invention is a method for manufacturing an enclosure defining a cavity, preferably hollow, the enclosure being intended to be applied against a sample to be analyzed, the cavity being configured to extend between the sample and an acoustic transducer, the cavity opening onto a contact face intended to be applied against the sample, the enclosure comprising: - a contact opening, provided in the contact face, leading into the cavity; - a membrane extending across the cavity, opposite the contact face, so that all or part of the cavity extends between the membrane and a cover;

[0009] the process comprising the steps: - 1) microstructuring of a first substrate, so as to form the hood; - 2) microstructuring of a second substrate, so as to form a part rear of the enclosure, delimiting all or part of the cavity, between the membrane and the cover; - 3) microstructuring of a third substrate, so as to form a part front of the enclosure, including the membrane; - 4) assembly of the cover onto the rear part of the enclosure, and of the part rear of the speaker on the front part of the speaker.

[0010] According to one possibility, the membrane separates the cavity into a rear portion of the cavity and a front portion of the cavity, the front portion of the cavity opening onto the contact face, the membrane being disposed between the front portion of the cavity and the rear portion of the cavity. Preferably, the front and rear portions of the cavity are hollow.

[0011] Step 2) may include a formation of the rear part of the cavity.

[0012] Step 3) may include a formation of the front part of the cavity.

[0013] Step 1) may include the formation of an acoustic channel extending through the hood, intended to connect the cavity to the acoustic transducer.

[0014] Step 1) may include the formation of a vent extending through the hood, intended to connect the cavity to an external environment.

[0015] Step 1) may include the formation of a detection channel, extending through the hood, intended to connect the cavity to a temperature and / or humidity sensor.

[0016] According to one possibility: - the first substrate comprises a first upper layer, a first intermediate layer (12), of insulating type, and a first lower layer; - step 1) includes • li) engraving of the first lower layer, so as to form at least one first lower opening, the first intermediate layer acting as an engraving stop layer; • lii) engraving of the first upper layer, so as to form at least one first upper opening, the first intermediate layer acting as an engraving stop layer; • liii) removal of the first intermediate layer, respectively between each first lower opening formed during substep li) and each first upper opening formed during substep lii), formed during substep lii), so as to form a channel, chosen from the acoustic channel, the vent or the detection channel.

[0017] Preferably, during steps li) and lii), at least two or three lower openings and at least two or three upper openings are formed respectively, so as to form two or three channels, during step liii), each channel corresponding to a channel chosen from the acoustic channel, the vent or the detection channel.

[0018] The first intermediate layer can be formed of an insulating material, the first upper layer and the first lower layer being formed of a semiconductor material.

[0019] According to one possibility: - the second substrate comprises a second upper layer, a second intermediate layer, and a second lower layer; - Step 2) includes the following sub-steps: • 2i) engraving of the second upper layer, so as to form a second upper opening, the second intermediate layer acting as an etching stop layer; • 2ii) etching of the second lower layer, so as to form a second lower opening, the second intermediate layer acting as an etching stop layer; • 2iü) removal of the second intermediate layer, respectively between the second upper opening formed during substep 2i) and the second lower opening formed during substep 2ii), so as to form all or part of the cavity.

[0020] According to one possibility: - the second substrate extends parallel to a main plane; - During step 2i), the engraving is carried out, through the second layer higher, according to a higher dimension, in the principal plane; - during step 2ii), the engraving is carried out, through the second lower layer, according to a smaller dimension, in the main plane; - the lower dimension is higher than the upper dimension.

[0021] The thickness of the second lower layer may be greater than the thickness of the second upper layer.

[0022] According to one possibility, the second intermediate layer is formed of an insulating material, the second upper layer and the second lower layer being formed of a semiconducting material.

[0023] According to one possibility, during step 2iii), the removal of the second intermediate layer forms the rear part of the cavity.

[0024] According to one possibility: - the third substrate comprises a third upper layer, a third intermediate layer and a third lower layer; - Step 3) includes: • 3i) engraving of the third lower layer, so as to form a front part of the speaker, the third intermediate layer acting as a recording stop layer, the third upper layer forming the membrane.

[0025] During step 3i), the etching of the third lower layer can form the front part of the cavity.

[0026] According to one possibility, the membrane is traversed by openings. The method may then comprise: - 3ii) etching of the third upper layer, the third intermediate layer acting as an etching stop layer, the etching of the third upper layer being configured to form a plurality of third openings extending through the third upper layer; - 3iii) removal of the third intermediate layer, at the level of each third opening resulting from sub-step 3ii), so that each third opening is through.

[0027] According to one possibility, each assembly is carried out by thermocompression.

[0028] A second object of the invention is an enclosure, delimiting a cavity, the enclosure being intended to be applied against a sample to be analyzed, the cavity being configured to extend between the sample and an acoustic detector, the cavity opening onto a contact face intended to be applied against the sample, the enclosure comprising: - a contact opening, provided in the contact face, leading into the cavity; - a membrane extending across the cavity, opposite the contact face, so that all or part of the cavity extends between the membrane and a cover;

[0029] the enclosure being manufactured by implementing steps 1) to 4) of the first object of the invention.

[0030] A third object of the invention is a device comprising an enclosure, delimiting a cavity, the enclosure being intended to be applied against a sample to be analyzed, the device comprising: - a contact face, opening into the cavity, and intended to be applied against the sample; - a light source, configured to emit pulsed or amplitude-modulated light through the enclosure, towards the contact face; - an acoustic transducer, connected to the cavity; - the device being such that the enclosure is an enclosure according to the second object of the invention.

[0031] The invention will be better understood upon reading the description of the exemplary embodiments presented later in this description, in connection with the figures listed below. FIGURES

[0032] Fig. 1 represents an overview of a photoacoustic detection device.

[0033] Figures 2A to 2T schematically illustrate the shaping steps of a first substrate, intended to form a hood of the device.

[0034] Figures 3A to 3Q schematically illustrate the shaping steps of a second substrate, intended to form a rear part of an enclosure of the device.

[0035] Figures 4A to 4K schematically illustrate the shaping steps of a third substrate, intended to form a front part of an enclosure of the device.

[0036] Figures 5A to 5D show the assembly steps of the first substrate, the second substrate and the third substrate after their shaping. PRESENTATION OF SPECIFIC IMPLEMENTATION METHODS

[0037] Figure 1 schematically illustrates a device 1 for implementing the invention. The device 1 is configured to be applied against a sample E to be analyzed. The device comprises a contact face 3, intended to be applied against the sample to be analyzed. The contact face is designed to conform to the sample E against which it is intended to bear. For example, it is flat.

[0038] In this example, the sample E is the skin of a user. The device includes a light source S, configured to emit a light beam L propagating to the sample E to be analyzed. The light source S is pulsed or amplitude-modulated. The light beam L is emitted in a spectral emission band AX comprising an absorption wavelength X, of molecules M present in the sample. One objective of the device 1 is to detect the presence of molecule M and possibly to estimate its concentration.

[0039] The molecule M can for example be glucose, or a body analyte such as cholesterol, triglycerides, urea, albumin, alcohol (for example ethanol), tetrahydrocannabinol.

[0040] The emission spectral band AX preferably extends in the visible or infrared range, for example between wavelengths of 3 pm and 15 pm. Preferably, the emission spectral band AX is sufficiently narrow so that the device 1 is specific to a single analyte. When the analyte is glucose, the emission spectral band is centered on a glucose absorption wavelength, for example corresponding to a wavenumber of 1034 cm⁻¹. The light source S may, in particular, be a pulsed laser source, for example a wavelength-tunable QCL (Quantum Cascade Laser). The emission spectral band AX is then located in the infrared.

[0041] According to other embodiments, the light source S may be a filament-type source or a light-emitting diode. According to these embodiments, it is preferable to combine the light source S with a bandpass filter to define a sufficiently narrow emission spectral band centered on the considered absorption wavelength. However, the use of a laser source is preferred.

[0042] The device comprises a containment chamber 2, positioned in contact with the sample E, and defining a cavity 4. The cavity 4 opens into a contact aperture 3o formed in the contact face 3, the contact aperture being intended to be applied to the sample E, preferably in contact with it. The light beam L propagates to the sample E through the cavity 4 and the contact aperture 3o.

[0043] The device comprises a membrane 5 extending through the cavity 4, opposite the contact face 3, the membrane preferably having through-holes 5o. The membrane 5 separates the cavity 4 into a front portion 4a, comprising the contact face 3, and a rear part 4r, extending between the membrane 5 and a cover 2c. The cover 2c closes the cavity 4, being positioned opposite the membrane 5.

[0044] In [Fig. 1], a segmentation of enclosure 2 into three components has been materialized: - the hood 2c; - the rear part 2r, which confines the rear part of the cavity 4r; - the front part 2a, which includes the membrane 5 and the contact face 3.

[0045] According to the process described below, these three components are made separately and then assembled. In [Fig. 1], the dashed lines represent the separations between the three components.

[0046] The membrane 5 can be as described in US 11774347. The membrane 5 extends inside the cavity 4, at a non-zero distance d from the contact opening 3o. Indeed, during the implementation of the device, it is preferable that the membrane 5 not be in contact with the sample E. Positioning the membrane at a distance allows for maintaining an air gap between the contact opening 3o and the membrane 5. The distance between the membrane and the contact opening is preferably greater than 200 pm, or 500 pm. The thickness e of the membrane 5 is preferably between 100 pm and 1 mm, and preferably between 150 pm and 750 pm.

[0047] When the membrane 5 has through-holes 5o, these are sized to transmit the pressure modulation through the membrane 5, while blocking liquid droplets or dust. The through-holes 5o allow air communication between the front part 4a and the rear part 4r of the cavity 4. The diameter of the through-holes 5o is preferably between 10 µm and 50 µm, and preferably between 10 µm and 30 µm.

[0048] Due to the presence of a molecule M in the sample E, an acoustic wave W, called a photoacoustic wave, is formed. The photoacoustic wave W is an acoustic wave formed from the periodic heating of the medium by the incident light beam L, the latter being either pulsed or amplitude-modulated. A portion of the photoacoustic background W extends through the cavity 4 so as to be detected by an acoustic transducer T. The acoustic transducer T is connected to the cavity 4 by an acoustic channel 2T formed in the cover 2C. The acoustic transducer T can be a microphone, having a detection spectral range that includes the photoacoustic background frequency. The photoacoustic wave is amplitude-modulated according to the pulse or amplitude modulation frequency of the light source. Thus, at the acoustic transducer, the pressure is amplitude-modulated.

[0049] The device may include a detector D, configured to detect a temperature and / or a relative humidity level in the cavity. The detector D is connected to the cavity 4 by a detection channel 2D provided in the cover 2c.

[0050] The device may include a vent 2E, provided in the cover 2c, configured to connect the cavity 4 to an external medium, for example ambient air. Such a vent was described in US11674931. The vent may extend over a length of between 1 mm and 20 mm, and a diameter of between 100 µm and 500 µm.

[0051] Figures 2A to 2R show the fabrication steps of a first substrate 10, so as to form the hood 2c of the device. In [Fig. 2A], the first substrate is shown, which, in this example, is a silicon-on-insulator (SOI) substrate, comprising: - a first lower layer 11, called bulk, of Si, with a thickness of a few hundred pm, for example 725 pm, when the diameter of the substrate is 200 mm. - a first intermediate layer 12 of insulation (SiO2), with a thickness of a few tens of nm or a few pm, for example 1 or 2 pm; - a first upper layer 13 of silicon, and generally in monocrystalline Si, with a thickness of 225 pm.

[0052] The structuring steps of the first substrate 10 are, successively: - Formation of 11m and 13m marks on the first lower and upper layers by laser engraving. See [Fig. 2B]. These marks serve as registration marks for aligning photolithography masks. These marks are no longer shown in the following figures. - Deposition of a layer of SiO2 16 of SiO2, with a thickness between 3 pm and 5 pm, on the first lower layer 11 and deposition of a layer 14 of SiO2, with a thickness between 3 pm and 5 pm, on the first upper layer 13: cf. [Fig.2C], the [Fig.2C] being represented after turning over the substrate represented on the [Fig.2B]. - Deposition of a layer of photolithography resin 17 on the layer 16 then formation of a pattern by exposure. The pattern defines openings 17a in the resin layer 17: see [Fig.2D]. - Plasma etching of layer 16, so as to form openings 16a in layer 16, and removal of resin 17.Cf. [Fig.2E] - The substrate is flipped over and a layer of photolithography resin 15 is deposited onto the SiO2 layer 14, followed by the formation of a pattern by exposure. The pattern defines openings 15a in the resin layer 15: see [Fig. 2F], on which the substrate has been flipped over relative to [Fig. 2E]. Plasma etching of layer 14, so as to form openings 14a in layer 14, removal of resin 15 and inversion of the substrate. See [Fig. 2G] Plasma etching of the first lower layer 11, so as to form first lower openings lia in the latter, directly above each opening 16a. See [Fig. 2H]. The first lower openings lia are intended to form through channels, such as the acoustic channel, the detection channel and the vent previously described. Lamination of a polymer film (Revalpha tape, manufacturer Nitto 18) onto layer 16, closing the first lower openings made in the previous step. See [Fig. 2I]. Plasma etching of layer 13, so as to form first upper openings 13a in it, directly above each opening 14a resulting from the step described in relation to [Fig. 2G]. See [Fig. 2J], on which the substrate has been inverted relative to [Fig. 21]. During etching, the polymer film protects a support onto which the first substrate 10 is deposited. Removal of polymer film 18: See [Fig.2K]. Removal, by wet etching, of the first intermediate layer 12 of SiO2, between each first lower aperture 11a and each first upper aperture 13a: see [Fig. 2L]. This step allows the formation of 3 through channels 10a1, 10a2, 10a3, corresponding respectively to channels 2T, 2d, 2e described in connection with [Fig. 1]. This yields a first microstructured substrate 10', which has the structure necessary for the formation of the device's cover 2c. The first microstructured substrate 10' extends, according to its thickness, between a first upper face 10's, adjacent to the first upper layer 13, and a second lower face 10';, adjacent to the first lower layer 11. Deposition of a 19s, 19; layer of Ge-ZnS; this layer having an antireflective function, respectively on the first upper 10's and lower 10'i faces of the substrate 10'. See [Fig. 2M]. ZnS has an antireflective function, while Ge promotes the adhesion of ZnS to Si. Each 19s, 19; layer is formed of a 100 nm thickness of Ge and a 1067 nm thickness of ZnS. The deposition is carried out at 175°C. Next, a lOp plate, forming a handle, is used, comprising a 550 µm thick Si layer covered with a polymer layer, for example the Revalpha polymer mentioned earlier. Preferably, the polymer used is easily removable by means of heat. - The plate is shown in [Fig.2N]. The handle allows for handling of the substrate, for example from a substrate holder. - Apposition of the plate lOp against the substrate 10', on the side of the first upper face 10's: cf. [Fig.20], on which the substrate has been turned over relative to the [Fig.2M]. - Application, by lamination, of a polymer adhesive film 19', for example a SINR film (registered trademark - supplier Shin-Etsu MicroSi), 12µm thick. See [Fig. 2P]. The assembly undergoes annealing. - Exposure of the film 19', so as to leave only a peripheral part extending around the channels made in the substrate 10'.[Fig.2Q] - Removal of the handle lOp: see [Fig. 2R]. This step produces a substrate which, after thermocompression assembly, forms the cover 2c of the device's enclosure 2. The assembly step is described below, in relation to Figures 5A to 5D. The structuring of the first substrate 10 creates spaces for the acoustic transducer T, the light source S, and the temperature and / or humidity detector D. These spaces are indicated by dotted lines in [Fig. 2R].

[0053] Figures 2S and 2T respectively represent a top and bottom view of the hood 2c, which corresponds to the micro-structured substrate 10'.

[0054] Figures 3A to 3Q show the manufacturing steps of a second substrate 20, of in order to form the rear part 2r of the device enclosure. A second substrate 20 is used, which is a silicon-on-insulator (SOI) substrate, comprising: - a second lower layer 21, called bulk, of Si, with a thickness of a few hundred pm, for example 725 pm, when the diameter of the substrate is 200 mm. - a second intermediate layer 22 of insulation (SiO2), with a thickness of a few tens of nm or a few pm, for example 1 or 2 pm; - a second upper layer 23 of silicon, and generally in monocrystalline Si, with a thickness of 225 pm.

[0055] The structuring steps of the second substrate 20 are, successively: - Formation of 21m and 23m marks on the second lower and upper layers by laser engraving. See [Fig. 3A]. These marks allow for the alignment of photolithography masks. These marks are not shown in the following diagram. - Deposition of a layer of 26 SiO2, with a thickness between 3 pm and 5 pm, on the second lower layer 21 and deposition of a layer 24 of SiO2, of thickness between 3 pm and 5 pm, on the second upper layer 23: cf. [Fig.3B], on which the second substrate is reversed relative to [Fig.3A], - Deposition of a layer of photolithography resin 25 on the SiO2 layer 24 then formation, by exposure, of a pattern. The pattern defines an opening 25a in the resin layer 25: see [Fig.3C]. - Plasma etching of layer 24, so as to form an opening 24a in layer 24 and removal of resin 25. See [Fig. 3D] - Deposition of a photolithography resin layer 27 on the layer 26 followed by the formation of a pattern by exposure. The pattern defines an opening 27a, wider than the opening 24a, in the resin layer 27: see [Fig.3E], on which the second substrate is reversed relative to [Fig.3D]. - Plasma etching of layer 26, so as to form an opening 26a in layer 26, then removal of the resin 27 and flipping of the second substrate, and plasma etching of the second upper layer 23, so as to form a second upper opening 23a in the latter, directly above the opening 24a resulting from the step described in relation to [Fig. 3D]. See [Fig. 3F], in which the second substrate is flipped relative to [Fig. 3E]. The designation "second upper opening" refers to the fact that it is an opening made in the second upper layer 23.

[0056] Each layer of the second substrate extends along a principal plane P, as shown in [Fig. 2A]. The second upper opening 23a extends, parallel to the principal plane, along a higher dimension D23. - Deposition of a layer of photolithography resin 27' onto the remaining layer 26 following the etching described in [Fig. 3F], with part of the resin 27' covering the first layer 21. The overlap of layer 21 by the resin 27' is indicated by a bracket. Exposure of the resin 27' to form an opening 27'a in the layer 27'. See [Fig. 3G], in which the second substrate is inverted relative to [Fig. 3F]. - Partial plasma etching of the second lower layer 21, so as to form a second lower opening 21a in the latter, directly above the opening 27a resulting from the step described in the previous step. See [Fig. 3H]. Openings 21a and 23a are intended to form the rear part of the cavity. The designation "second lower opening" indicates that it is an opening made in the second lower layer 21. The second lower opening 21a extends, parallel to the main plane, along a smaller dimension D2b. Preferably, D2b > D23b. - Resin removal 27' cf. [Fig.31]. - Additional etching of layer 21, up to layer 22. This creates a step 21b on layer 21. Then, a polymer film 28 is deposited by lamination onto layer 24. See [Fig. 3J]. The polymer film 28 is of the same type as the film 18 described previously. - Removal, by wet etching, of the SiO2 layer 22: see [Fig.3K]. This step allows a through opening 20a to be formed. - Removal of the polymer film 28: See [Fig. 3L]. This yields a second microstructured substrate 20', which has the structure necessary for the formation of the rear part of the enclosure 2r. The second microstructured substrate 20' extends, according to its thickness, between a second upper face 2O'S, adjacent to the second upper layer 23, and a second lower face 2O';, adjacent to the second lower layer 21. - Next, a 20p plate, forming a handle, is used, comprising a 20p2 layer of Si 550pm thick covered with a layer of a 20pl polymer. The plate is placed against the second lower face 20'i of the second substrate 20' (see figures 3M and 3N). In [Fig.3M], the second substrate is reversed relative to [Fig.3L]. - Application, by lamination, of a polymer adhesive film 29' onto the second upper layer 23. The adhesive film can, for example, be a SINR film (registered trademark - supplier Shin-Etsu MicroSi) with a thickness of 12µm, then annealed. See [Fig. 30] - Exposure of film 29', so as to leave only a peripheral part extending around the opening 20a of the substrate 20', then annealing. See [Fig. 3P] - Removal of handle 20p: [Fig. 3Q], on which the second substrate is inverted relative to [Fig. 3P]. This step yields the rear part 2r of the enclosure, after assembly by thermocompression. The through-hole 20a forms the rear part 4r of cavity 4. The assembly step is described below, in connection with Figures 5A to 5C.

[0057] Figures 4A to 4J show the manufacturing steps of a third substrate 30, so as to form the front part 2a of the device enclosure. A third substrate 30 is used, comprising a lower third layer 31, an intermediate third layer 32 and an upper third layer 33 respectively similar to the lower, intermediate and upper layers of the first and second substrates previously described. See [Fig. 4A].

[0058] The structuring steps of the third substrate 30 are, successively: - Formation of 33m registration marks on the upper third layer by laser engraving. These registration marks allow for the alignment of photolithography masks. Then a layer 36 of SiO2, with a thickness between 3 pm and 5 pm, is deposited on the third lower layer 31 and a layer 34 of SiO2, with a thickness between 3 pm and 5 pm, is deposited on the third upper layer 33: see [Fig.4B] - Deposition of a photolithography resin layer 35 onto the SiO2 layer 34, followed by the formation of a pattern by exposure. The pattern defines openings 35a in the resin layer 35. Then, plasma etching of the layer 34 forms openings 34a in the layer 34. See [Fig. 4C]. The aim is to initiate the formation of through-holes in the layer 33, so as to form the membrane 5 described in connection with [Fig. 1]. - Plasma etching of the upper layer 33, so as to form openings 33a in it, directly above each opening 34a resulting from the previous step. See [Fig. 4D]. The steps shown in Figures 4C and 4D are optional. - Deposition of a layer of photolithography resin 37 on the layer 36 then formation of a pattern by exposure. The pattern defines an opening 37a. Cf. [Fig.4E], on which the third substrate is reversed relative to [Fig.4D]. - Plasma etching of layer 36, so as to form an opening 36a in layer 36, then removal of the resin 37. Cf. [Fig.4F] - Deposition, by lamination, of a polymer film 38, on layer 34. See [Fig. 4G]. The film 38 is of the same type as the films 18 and 28 previously described. - Plasma etching of the lower layer 31, so as to form an opening 31a in the latter, directly above the opening 36a resulting from the step described in connection with [Fig.4F]. Cf. [Fig.4H]. - Removal of the polymer film 38. See [Fig. 4I]. This yields a third microstructured substrate 30', which has the structure necessary for the formation of the front part 2a of the enclosure. The third microstructured substrate 30' extends, according to its thickness, between a third upper face 30's, adjacent to the third upper layer 33, and a third lower face 30'i, adjacent to the third lower layer 31. - Deposition of an antireflective layer 39s, 39; of Ge-ZnS comprising a thickness of 100nm of Ge and 1067nm of ZnS on the third upper face and the third lower face of the substrate 30' respectively. Cf. [Fig.4J]. This step allows us to obtain the front part 2a of the enclosure 2 of the device, which includes the membrane.

[0059] Figure 4K shows a top view of the substrate 30': the through openings 30a can be seen, which, after assembly, correspond to the openings 50 of the membrane. In this example, the through-holes have a diameter of 30 pm, with a spacing of 100 pm between two adjacent openings. In [Fig. 4K], the unit for each axis is the millimeter.

[0060] In the embodiment shown in Figures 4A to 4K, the membrane has openings and is recessed from the contact face. The membrane defines a hollow front portion of the cavity: the front portion of the cavity extends between the contact face and the membrane. According to one variant, the etching of the lower third layer 31 is such that, following the step shown in [Fig. 4H], the membrane is flush with the contact face. According to this variant, it is preferable that the membrane not be hollow: it is intended to be positioned in contact, or near-contact, for example, less than 1 mm, less than 500 µm, or less than 100 µm, with the sample.

[0061] Figures 5A to 5D show the thermocompression assembly steps used to form the enclosure 2 of the device shown in [Fig. 1], by: - assembly of the rear part 2r on the front part 2a: the second upper face 2O'S of the second substrate 20' is joined, by the polymer 29', to the third upper face 30's of the third substrate 30': see figures 5A and 5B: a substrate 2ar is obtained; - Assembly of the cover 2c onto the substrate 2ar: the second lower face 20'i of the second substrate 20' is bonded, by the polymer 19', to the first lower face 10'i of the first substrate 30' (see Figures 5C and 5D): this results in an assembled substrate, forming the enclosure 2 of the device. Figure 5D shows the main components of the enclosure, as described in relation to Figure 1. The location of the transducer T, the light source S, and the detector D is also shown schematically.

[0062] Each assembly is carried out, for example, by thermocompression, using polymer adhesive 19', 39'. Other adhesives may be used, organic or inorganic.

[0063] The order of assembly can be reversed.

[0064] The process described above can be replicated on the same substrate, in parallel, so as to simultaneously form several enclosures 2. This yields several enclosures 2, which can be separated from one another after all the manufacturing steps, according to a pick-and-place process. Bonding can be performed in wafer-level mode (plate-to-plate), die-to-wafer mode (chip-to-plate), or flip-chip mode (chip-on-chip).

[0065] The use of microfabrication processes makes it possible to obtain a compact device, compatible with integration into a portable object, for example a smartwatch. The volume of enclosure 2 can be on the order of a few tenths of a cubic centimeter. The process can be implemented using standard silicon substrates.

[0066] Using a thermocompression assembly with a polymer avoids the difficulties associated with metallic bonding, which has a low yield and depends on the surface condition of the surfaces being joined. Alternatively, the three substrates can be joined using metallic bonding of the Ti-Ti or Au-Au type. In this case, the parts to be joined are metallic.

[0067] The use of three independent substrates allows for modification of one of them without affecting the manufacture of the others. For example, the first substrate, forming the cover, can be modified while remaining compatible with the second and third substrates, forming the front and rear sections of the enclosure. Similarly, the configuration of the membrane (third substrate) can be modified while remaining compatible with the first and second substrates, forming the cover and the rear section of the enclosure.

[0068] The use of three independent substrates also makes it possible to consider parallel manufacturing.

[0069] Although described in connection with SOI substrates, which corresponds to an advantageous configuration because each intermediate insulator layer can be used as an etching stop layer, the use of other types of substrates, of the "bulk" type, is conceivable.

Claims

Demands

1. Method of manufacturing an enclosure (2) delimiting a hollow cavity (4), the enclosure being intended to be applied against a sample to be analyzed (E), the cavity being configured to extend between the sample and an acoustic transducer (T), the cavity opening onto a contact face (3) intended to be applied against the sample, the enclosure comprising: - a contact opening (3o), formed in the contact face, opening into the cavity; - a membrane (5) extending through the cavity, opposite the contact face, so that all or part of the cavity extends between the membrane and a hood (2c); the method comprising the steps: - 1) microstructuring of a first substrate (10), so as to form the hood (2c); - 2) micro structuring of a second substrate (20), so as to form a rear part of the enclosure (2r), delimiting all or part of the cavity, between the membrane and the hood;- 3) microstructuring of a third substrate (30), so as to form a front part (2a) of the enclosure, comprising the membrane; - 4) assembly of the cover (2c) onto the rear part of the enclosure (2r), and of the rear part of the enclosure (2r) onto the front part of the enclosure (2a).

2. A method according to claim 1, wherein the membrane (3) separates the cavity between a rear part of the cavity (4r) and a front part of the cavity (4a), the front part of the cavity opening onto the contact face, the membrane being disposed between the front part of the cavity and the rear part of the cavity, the method being such that: - step 2) comprises a formation of the rear part of the cavity; - step 3) comprises a formation of the front part of the cavity.

3. A method according to any one of the preceding claims, wherein step 1) comprises the formation of an acoustic channel (2T) extending through the hood, intended to connect the cavity to the acoustic transducer.

4. A method according to any one of the preceding claims, wherein step 1) comprises the formation of a vent (2E) extending through the hood, intended to connect the cavity to a medium external to the latter.

5. A method according to any one of the preceding claims, wherein step 1) comprises forming a (2D) sensing channel extending through the hood, intended to connect the cavity to a temperature and / or humidity sensor

6. A method according to any one of claims 1 or 2, and any one of claims 3 to 5, wherein: - the first substrate comprises a first upper layer (13), a first intermediate layer (12), of insulating type, and a first lower layer (11); - step 1) comprises: • 1) etching the first lower layer, so as to form at least one first lower opening (1a), the first intermediate layer acting as an etching stop layer; • 11) etching the first upper layer, so as to form at least one first upper opening (13a), the first intermediate layer acting as an etching stop layer;• liii) removal of the first intermediate layer, respectively between each first lower opening formed during substep li) and each first upper opening formed during substep lii), so as to form a channel, chosen from the acoustic channel, the vent or the detection channel.;

7. A method according to claim 6, wherein the first intermediate layer is formed of an insulating material, the first upper layer and the first lower layer being formed of a semiconducting material.

8. A method according to any one of the preceding claims, wherein: - the second substrate comprises a second upper layer (23), a second intermediate layer (22), and a second lower layer (21); - step 2) comprises the following sub-steps: • 2i) etching the second upper layer, so as to form a second upper opening (23a), the second intermediate layer acting as an etching stop layer; • 2ii) etching the second lower layer, so as to form a second lower opening (21a), the second intermediate layer acting as an etching stop layer; • 2iii) removing the second intermediate layer, respectively between the second upper opening formed during sub-step 2i) and the second lower opening formed during sub-step 2ii), so as to form all or part of the cavity.

9. A method according to claim 8, wherein: - the second substrate extends parallel to a principal plane (P); - in step 2i), the engraving is carried out, through the second upper layer, along a higher dimension (D2 3), in the principal plane; - in step 2ii), the engraving is carried out, through the second lower layer, along a lower dimension (D2 i), in the principal plane; - the lower dimension is higher than the upper dimension.

10. A method according to any one of claims 8 or 9, wherein the thickness of the second lower layer is greater than the thickness of the second upper layer.

11. A method according to any one of claims 8 to 10, wherein the second intermediate layer is formed of an insulating material, the second upper layer and the second lower layer being formed of a semiconducting material.

12. A method according to any one of claims 8 to 10, and according to claim 2, wherein during step 2iii), the removal of the second intermediate layer forms the rear part of the cavity.

13. A method according to any one of the preceding claims, wherein: - the third substrate comprises a third upper layer (33), a third intermediate layer (32) and a third lower layer (31); - step 3) comprises: • 3i) etching the third lower layer, so as to form a front part of the enclosure, the third intermediate layer acting as an etching stop layer, the third upper layer forming the membrane.

14. A method according to claim 13, and according to claim 2, wherein in step 3i), the etching of the third lower layer forms the front part of the cavity (4a).

15. A method according to any one of the preceding claims, wherein the membrane is traversed by openings.

16. A method according to claim 15 and any one of claims 13 and 14, comprising: - 3ii) etching the third upper layer, the third intermediate layer acting as an etching stop layer, the etching of the third upper layer being configured to form a plurality of third openings extending through the third upper layer; - 3iii) removing the third intermediate layer, at each third opening resulting from substep 3ii), so that each third opening is through.

17. A method according to any one of the preceding claims, wherein each assembly is carried out by thermocompression.

18. Enclosure (2), delimiting a cavity (4), the enclosure being intended to be applied against a sample to be analyzed (E), the cavity being configured to extend between the sample and a detector

19. acoustic, the cavity opening onto a contact face (3) intended to be applied against the sample, the enclosure comprising: - a contact opening (3o), provided in the contact face, opening into the cavity; - a membrane (5) extending through the cavity, opposite the contact face, so that all or part of the cavity extends between the membrane and a cover (2c); the enclosure being manufactured by implementing steps 1) to 4) of any of the preceding claims. A device comprising an enclosure (2), delimiting a cavity (4), the enclosure being intended to be applied against a sample to be analyzed (E), the device comprising: - a contact face, opening into the cavity, and intended to be applied against the sample; - a light source (S), configured to emit pulsed or amplitude-modulated light through the enclosure, towards the contact face; - an acoustic transducer, connected to the cavity; - the device being such that the enclosure is an enclosure according to claim 18.

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