Method for sealing a cavity using a membrane

Abstract

The present invention relates to a method for sealing a cavity (11) using a membrane, the method comprising: (a) forming cavities (11) with a depth p and a characteristic dimension a, arranged in a matrix and spaced apart by a distance b; and (b) forming the membrane and sealing the cavities (11) by transferring a sealing film, the method comprising, prior to step (b), a step (a1) of forming a first contour on the front surface (10a) and / or the sealing surface (16a), the first contour comprising a first trench (21) having a width L and a depth p1; and, after step (b), forming the first contour is performed such that the cavity (11) is circumscribed by the first contour, the first contour being at a distance G from the cavity that is between one-fifth b and 5b.

Description

[Technical Field]

[0001] The present invention relates to the field of substrates and / or microelectromechanical systems, in particular for detecting gases or more generally for manufacturing membrane-based transducer devices, in particular ultrasonic transducers.

[0002] In particular, the present invention relates to a method for collectively fabricating multiple membranes that seal a cavity.

[0003] The method according to the invention comprises the formation of a first contour, particularly advantageously comprising a continuous first trench, formed around the arrangement of cavities intended to be sealed by the membrane, this contour being used in particular to damp or concentrate the deformations to which the membrane is prone during its formation. [Background technology]

[0004] The use of suspended membranes is of growing interest both in the field of microelectromechanical systems (MEMS) and in the field of substrates, especially temporary substrates.

[0005] These membranes formed by the sealing films advantageously seal cavities, in particular cavities created in the surface of the support substrate.

[0006] A method known from the prior art for forming a membrane sealing a cavity is shown in Figures 1a to 1c.

[0007] The method includes, inter alia, the following steps: (i) providing a donor substrate 1 and a receiving substrate 2 with cavities 31, 32 opening on the front surface 2a of the receiving substrate 2; (ii) assembling the donor substrate 1 and the receiving substrate 2 to seal the cavity 3; (iii) Thinning the donor substrate 1 so as to retain only a portion of the substrate 1, called the sealing film 4, to form a set of films 41, 42 etc.

[0008] The thinning step (iii), which is generally carried out by mechanical etching (milling) and / or chemical etching, ensures the consumption of the donor substrate.

[0009] Furthermore, the uniformity of the sealing film after step (iii), which is highly dependent on the technology used in step (iii), remains difficult to control.

[0010] Furthermore, the sealing film portion that is vertical in the cavity is not subjected to back pressure from the cavity, and therefore, if step (iii) involves mechanical thinning, it is not possible to envisage obtaining very thin films, e.g., less than 5 μm thick, without risking breaking the film.

[0011] To overcome the problems associated with obtaining uniformity and thin films, the donor substrate can be made removable (as shown in Figure 2a).

[0012] Such a donor substrate 1 comprises in particular a layer called a barrier layer 5 interposed between the mechanical support 6 and the sealing film 4, intended to form membranes 41, 42 after step (iii).

[0013] The barrier layer 5 can in particular be etched selectively with respect to the encapsulation film, so that the film thickness uniformity is only slightly or not affected by the thinning step (FIG. 2c).

[0014] For example, if the membrane comprises silicon, the detachable donor substrate can be a silicon-on-insulator (SOI) type substrate.

[0015] However, such substrates, the "removal" of which also results in the consumption of mechanical support and barrier layers, have costs that are incompatible with the requirements of the microelectronic and / or micromechanical industry.

[0016] Alternatively, or in addition, the cavities formed during step (i) (FIG. 3a) can be filled with a sacrificial material 7 intended to be removed after step (iii) during step (iv) (FIGS. 3c and 3d). However, this latter step requires the formation of openings in each of the membranes and their sealing after the removal of the sacrificial material (FIG. 3e). Therefore, this latter approach remains complex and prone to causing changes in the mechanical behavior of the membranes.

[0017] The so-called "Smart-Cut™" approach, described in EP 533551, can also be considered.

[0018] This approach allows for the transfer of encapsulation films by separating them from a substrate, called a donor substrate, at a weakened region. The weakened region formed by implantation and / or amorphization allows for the demarcation of relatively thin encapsulation films (especially those with a thickness of less than 2 μm, e.g., 1.5 μm). Furthermore, the "Smart-Cut™" approach paves the way for reusing the donor substrate to transfer the encapsulation film again.

[0019] The membranes formed by the sealing film have non-uniform deformation from one membrane to another when the latter is formed on an array of cavities, especially a matrix array.

[0020] More specifically, the deformation increases from the center to the edge of the membrane array.

[0021] In this regard, Figures 4a and 4b show, respectively, an image obtained using optical interferometry and a deformation profile of a membrane formed according to a matrix alignment by the Smart-Cut™ method.

[0022] These two figures show very clearly the non-uniformity of deformation from one membrane to another.

[0023] Furthermore, the deformation of these membranes increases as the thickness of the sealing film increases.

[0024] This effect is depicted graphically in Figure 5. In particular, Figure 5 shows the observed amplitude of membrane deformation (in "nm" along the vertical axis) for sealing film thicknesses of 1.5 μm (A), 0.85 μm (B), and 0.2 μm (C) according to bonding conditions (conditions "1," "2," "3," and "4" along the horizontal axis).

[0025] This variability also depends on the membrane's environment, especially its immediate environment: the greater the distance from other membranes, the greater the deformation.

[0026] Finally, this variability also depends on the position of the cavity matrix on the receiving substrate 2. Figure 6A shows a graphical representation of the deformation of the membrane for a matrix located in the center of the substrate and for a matrix located at the edge (Figure 6B). In particular, a greater variability in deformation can be observed for a matrix located near the edge of the receiving substrate (Figure 6A, curve D) compared to the same matrix located near the center of the substrate (Figure 6A, curve E).

[0027] The variability of these deformations generates different electromechanical behaviors of the membranes of, for example, MEMS or NEMS type devices.

[0028] It may also make subsequent technological steps much more uneven, complicated, or even impossible to carry out. [Prior art documents] [Patent documents]

[0029] [Patent Document 1] European Patent No. 533551 Summary of the Invention [Problem to be solved by the invention]

[0030] It is an object of the present invention to provide a method for sealing multiple cavities using a membrane, which makes it possible to reduce the deformation differences between them. [Means for solving the problem]

[0031] The object of the present invention is achieved by a method for sealing multiple cavities using multiple membranes, the method comprising the following steps: (a) forming a plurality of cavities opening onto a front surface of the support substrate or onto a sealing surface of the sealing film, the cavities advantageously being arranged in a matrix, having a depth p, a characteristic dimension a and being spaced apart by a spacing b; (b) transferring a sealing film overlying the front surface to form a plurality of membranes and seal each of the cavities, before the transferring includes assembling the sealing surface with the front surface; Including, The method comprises a step (a1) carried out before step (b) of forming a first contour on one and / or the other of the front surface and the sealing surface, the first contour comprising a preferably continuous first trench having a width L and a first depth p1, and the formation of the first contour is carried out such that after step (b) the plurality of cavities are circumscribed by the first contour, the first contour being preferably at an essentially constant distance G from the plurality of cavities between one-fifth b and 5b, preferably between half b and 2b, more preferably between 0.9 x b and 1.1 x b.

[0032] According to one embodiment, the width L is between one-fifth of a and 5a, advantageously between half a and 2a, and more advantageously between 0.9×a and 1.1×a.

[0033] According to one embodiment, the cavity is square, circular or polygonal in shape, in particular hexagonal in shape.

[0034] According to one embodiment, the first depth p1 is equal to the depth p of the cavity.

[0035] According to one embodiment, a first contour is formed on the front surface, and step (b) is followed by step (c) of partially removing the sealing film (16) to reveal the first contour, said partial removal retaining a portion of the sealing film circumscribed by the first contour.

[0036] According to one embodiment, the first contour is formed in the sealing surface, and the first depth p1 is less than the thickness of the sealing film.

[0037] According to one embodiment, the first contour is formed on the sealing surface, and the first depth p1 is equal to or greater than the thickness of the sealing film, such that the first contour is exposed to the external environment after step (b).

[0038] According to one embodiment, step (a1) also comprises forming at least one second contour comprising a second trench or a series of second cavities at an essentially constant distance from the first contour, advantageously around the first trench at all points.

[0039] According to one embodiment, the depth of the at least one second contour, referred to as second depth p2, is equal to depth p.

[0040] According to one embodiment, the first contour and at least the second contour are linked by one or more interconnecting channels.

[0041] According to one embodiment, one or more interconnecting channels link two adjacent corners of the first and second contours, respectively.

[0042] According to one embodiment, the method comprises a step (b1) of bonding a donor substrate with a support substrate, the donor substrate comprising a sealing film resting on a handle substrate, followed by a step (b2) of removing the handle substrate.

[0043] According to one embodiment, step (b2) comprises etching by mechanical and / or chemical abrasion.

[0044] According to one embodiment, the donor substrate includes an intermediate layer interposed between the handle substrate and the sealing film, the intermediate layer having etch selectivity to the sealing film and the handle substrate.

[0045] According to one embodiment, the donor substrate includes embrittled regions that delimit the encapsulation film and are configured to break upon application of mechanical stress and / or heat treatment.

[0046] According to one embodiment, the embrittled region is obtained by implantation of seeds.

[0047] According to one embodiment, the encapsulation film comprises a semiconductor material, advantageously the semiconductor material comprises at least an element selected from silicon, germanium, a silicon and germanium alloy, indium phosphide, a III-V semiconductor arsenide, a III-V semiconductor phosphide, or a III-V semiconductor nitride, silicon carbide.

[0048] According to one embodiment, the sealing film comprises a metallic material, advantageously comprising at least an element selected from aluminum, copper, titanium, tungsten, tungsten silicide, gold.

[0049] According to one embodiment, the sealing film comprises an insulating material, advantageously the insulating material comprises at least an element selected from silicon dioxide, silicon nitride.

[0050] According to one embodiment, the sealing film comprises a piezoelectric material, advantageously the piezoelectric material comprises at least an element selected from lithium tantalate, lithium niobate, aluminum nitride, zinc oxide, zinc and lead tantalate.

[0051] The invention also relates to the use of the method according to the invention for manufacturing microelectromechanical systems.

[0052] According to one embodiment, the microelectromechanical system is a capacitive ultrasonic transducer.

[0053] The present invention also provides a device comprising multiple cavities sealed using multiple membranes, comprising: This device, (a) a plurality of cavities opening onto the front surface of the support substrate or the sealing surface of the sealing film, the cavities being advantageously arranged in a matrix, having a depth p, a characteristic dimension a, and being spaced apart by a distance b; (b) a plurality of membranes sealing each of the cavities formed by a sealing film assembled with the front surface using its sealing surface; Equipped with The device is characterized in that it comprises a first contour of width L on one and / or the other of the front and sealing surfaces, the first contour comprising a first trench, a plurality of cavities being circumscribed by the first contour, the first contour being advantageously at an essentially constant distance G from the plurality of cavities and being arranged so as to be between one-fifth b and 5b, advantageously between one-half b and 2b, more advantageously between 0.9 x b and 1.1 x b.

[0054] Further features and advantages will become apparent in the following description of a method for sealing a cavity using a membrane, given by way of non-limiting example, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0055] [Figure 1a] 1 is a diagram of the various steps of a method for forming a membrane known from the prior art; [Figure 1b] 1 is a diagram of the various steps of a method for forming a membrane known from the prior art; [Figure 1c] 1 is a diagram of the various steps of a method for forming a membrane known from the prior art; [Figure 2a] 1 is a diagram of the various steps of a method for forming a membrane known from the prior art; [Figure 2b] 1 is a diagram of the various steps of a method for forming a membrane known from the prior art; [Figure 2c] 1 is a diagram of the various steps of a method for forming a membrane known from the prior art; [Figure 3a] 1 is a diagram of the various steps of a method for forming a membrane known from the prior art; [Figure 3b] 1 is a diagram of the various steps of a method for forming a membrane known from the prior art; [Figure 3c] 1 is a diagram of the various steps of a method for forming a membrane known from the prior art; [Figure 3d] 1 is a diagram of the various steps of a method for forming a membrane known from the prior art; [Figure 3e] 1 is a diagram of the various steps of a method for forming a membrane known from the prior art; [Figure 4a] Image obtained by optical interferometry of a matrix array of multiple films (grayscale is height dependent). [Figure 4b] 1 is a graphical representation of the deformation D of the membrane (along the vertical axis, in "nm") with the position X of the membrane (increasing from the edge towards the center, horizontal axis, "μm"). [Figure 5] The observed membrane deformation amplitudes (along the vertical axis, "nm") for sealing film thicknesses of 1.5 μm (A), 0.85 μm (B), and 0.2 μm (C) are shown according to the bonding conditions (conditions "1," "2," "3," and "4" along the horizontal axis). [Figure 6A] 1 is a graphical representation of the deformation of the film (vertical axis, "nm") as a function of the film's position on the matrix (horizontal axis), where curves D and E relate to the matrix near the edge of the receiving substrate and the matrix near the center of the receiving substrate, respectively. [Figure 6B] 1 is a schematic diagram of a substrate comprising a first arrangement E and a second arrangement D of a membrane. [Figure 7a] 3 is a diagram of various steps of a method according to a first alternative embodiment of the first embodiment of the invention; [Figure 7b] 3 is a diagram of various steps of a method according to a first alternative embodiment of the first embodiment of the invention; [Figure 7c]3 is a diagram of various steps of a method according to a first alternative embodiment of the first embodiment of the invention; [Figure 8a] 5 is a diagram of various steps of a method according to a second alternative embodiment of the second embodiment of the invention; [Figure 8b] 5 is a diagram of various steps of a method according to a second alternative embodiment of the second embodiment of the invention; [Figure 8c] 5 is a diagram of various steps of a method according to a second alternative embodiment of the second embodiment of the invention; [Figure 9a] It represents a matrix arrangement of cavities surrounded by trenches. [Figure 9b] FIG. 9b is a close-up view of the upper left corner of the matrix array of FIG. 9a. [Figure 10a] 1 is a partial illustration of a matrix surrounded by a first trench and a second trench, with or without an interconnect channel, respectively. [Figure 10b] 1 is a partial illustration of a matrix surrounded by a first trench and a second trench, with or without an interconnect channel, respectively. [Figure 11a] 1 is an image obtained using an optical microscope that makes it possible to observe the effect of the first trench 21 on the deformation of the membrane relative to the deformation observed in the absence of a trench, and in particular represents an image of a membrane formed in the absence of a trench. [Figure 11b] 1 is an image obtained using an optical microscope that makes it possible to observe the effect of the first trench 21 on the deformation of the membrane relative to the deformation observed in the absence of a trench, and in particular represents an image of the membrane formed in the presence of a trench. [Figure 12a] FIG. 11a represents a measurement using optical interferometry of the area involved. [Figure 12b] FIG. 11b represents a measurement using optical interferometry of the relevant area. [Figure 13a] 3 is a diagram of various steps of a method according to a first aspect of a second embodiment of the invention (according to a first alternative embodiment); [Figure 13b]3 is a diagram of various steps of a method according to a first aspect of a second embodiment of the invention (according to a first alternative embodiment); [Figure 14a] 3 is a diagram of various steps of a method according to a first aspect of a second embodiment of the invention (according to a first alternative embodiment); [Figure 14b] 3 is a diagram of various steps of a method according to a first aspect of a second embodiment of the invention (according to a first alternative embodiment); [Figure 15] 10 is a diagrammatic representation of the transferring step (b) according to a first aspect of the second embodiment (first and second alternative embodiments); [Figure 16a] 4 is a diagram of various steps of a method according to a second aspect of the second embodiment of the invention (according to a second alternative embodiment); [Figure 16b] 4 is a diagram of various steps of a method according to a second aspect of the second embodiment of the invention (according to a second alternative embodiment); [Figure 17a] 4 is a diagram of various steps of a method according to a second aspect of the second embodiment of the invention (according to a second alternative embodiment); [Figure 17b] 4 is a diagram of various steps of a method according to a second aspect of the second embodiment of the invention (according to a second alternative embodiment); [Figure 18] 10 is a diagrammatic representation of the transferring step (b) according to a second aspect of the second embodiment (first and second alternative embodiments); [Figure 19a] 4 is a diagrammatic representation of various steps of a method according to a third aspect of the second embodiment of the invention (according to a second alternative embodiment); [Figure 19b] 4 is a diagrammatic representation of various steps of a method according to a third aspect of the second embodiment of the invention (according to a second alternative embodiment); [Figure 20] FIG. 10 is a diagram of the transferring step (b) according to the third aspect of the second embodiment (first and second alternative embodiments). [Figure 21a] In particular, it is a schematic diagram of an array of cavities surrounded by a first discontinuous trench, with four cross sections each located near one side of the array of cavities. [Figure 21b] In particular, it is a schematic diagram of an array of cavities surrounded by a first discontinuous trench, the first discontinuous trench having four discontinuous cross sections each located near one side of the array of cavities. [Figure 22] The graph shows the average membrane deformation (in "nm" on the vertical axis) as a function of the spacing b (in "μm" on the horizontal axis). DETAILED DESCRIPTION OF THE INVENTION

[0056] The present invention proposes a method for sealing cavities arranged in a matrix using a membrane, for example. The method according to the invention comprises in particular the transfer of a sealing film intended to form the membrane.

[0057] Furthermore, in order to ensure a more uniform and limited deformation of the membrane sealing the cavities, the method according to the invention comprises a step of forming a first contour comprising an advantageously continuous first trench surrounding the array of cavities.

[0058] 7a to 7c and 8a to 8c show the various steps of a method for sealing a cavity according to a first embodiment of the invention.

[0059] The method includes, inter alia, a step (a) of forming a plurality of cavities 11 opening onto the front surface 10a of a support substrate 10 (FIG. 7a).

[0060] The remainder of the present disclosure also relates to the use of a sealing film on the front surface 10a, intended for transfer using one of its surfaces, referred to as the sealing surface. According to another aspect of this first embodiment, it can be considered to form a plurality of cavities 11 on the sealing film, in particular cavities opening into the sealing surface. After merely reading the following description, a person skilled in the art will be able to implement this other aspect.

[0061] The cavities 11 can, for example, be arranged in a matrix (FIG. 9a).

[0062] The term "matrix arrangement" refers to a regular arrangement along two different, for example perpendicular, directions of identical cavities 11. The matrix arrangement may in particular include n rows and m columns of cavities 11.

[0063] Therefore, the matrix arrangement according to the present invention is not limited to a periodic arrangement along two orthogonal directions of rows and columns, and may include other matrix shapes, such as a hexagonal arrangement or a circularly symmetric arrangement organized in concentric circles.

[0064] The cavities 11 have a depth p, a characteristic dimension a, and are spaced apart by a spacing b. For example, if an arrangement according to a rectangular matrix is ​​considered, the spacing b is defined along one and the other of the directions defined by the columns and rows of the cavity matrix (FIG. 9b).

[0065] The spacing b according to the invention corresponds, for example, to the average spacing of the cavities in the random array.

[0066] "Characteristic dimension" refers to the largest dimension of the cavity opening. The opening may be circular, square, rectangular or more generally have n sides, for example polygonal, in particular triangular or hexagonal.

[0067] The shape of a cavity according to the present invention is defined by the shape of its opening.

[0068] For example, the cavity 11 may have a square shape with a side a of 0.5 μm to 500 μm and a depth p of 10 nm to 10 μm.

[0069] The spacing b is advantageously between 1 μm and 500 μm.

[0070] The matrix array can contain hundreds or thousands of cavities.

[0071] It can be seen that the array is bounded by a contour defined by the peripheral cavity of said array (FIG. 9a).

[0072] The support substrate may comprise a semiconductor material, advantageously the semiconductor material comprising at least an element selected from silicon, germanium, a silicon and germanium alloy, indium phosphide, a III-V semiconductor arsenide, a III-V semiconductor phosphide or a III-V semiconductor nitride, silicon carbide.

[0073] The support substrate may comprise a metallic material, which advantageously comprises at least an element selected from aluminium, copper, titanium, tungsten, tungsten silicide, gold.

[0074] The support substrate may comprise an insulating material, which advantageously comprises at least an element selected from silicon dioxide, silicon nitride.

[0075] The encapsulation film may comprise a piezoelectric material, advantageously the piezoelectric material comprises at least an element selected from lithium tantalate, lithium niobate, aluminium nitride, zinc oxide, zinc and lead tantalate.

[0076] Step (a) may in particular include a masking step for delineating the cavity 11 and an etching step.

[0077] The masking step may involve the formation of a hard mask, particularly a silicon dioxide mask.

[0078] The etching step can include dry etching (eg, etching involving plasma) or wet etching.

[0079] The method also includes the step (a1) of forming a first contour.

[0080] "First contour" refers to a path, advantageously a closed path, formed by one or more structures recessed relative to the surface of the support on which it is formed. The first contour has a width L, in particular defined by the structures.

[0081] The width L of the contours throughout the description corresponds to an average length. More specifically, the sidewalls of the trench that form the contours can have varying spacing. For example, one and / or the other of these walls can outline a sawtooth profile or have irregularities that cause width variations.

[0082] "Recessed" refers to a structure having a first depth p1.

[0083] The first contour may include one or more advantageously continuous first trenches.

[0084] 21a and 21b show first contours formed by first discontinuous trenches, which may in particular include four portions each near one side of the array of cavities.

[0085] The remainder of the disclosure of this first embodiment is limited to the first contour formed by the first continuous trench.

[0086] According to this first embodiment, a first trench 21 is formed on the support substrate 10 and is open at the front side 10a.

[0087] In particular, the first trench surrounds the array of cavities.

[0088] The first trench 21 has a width L and is at an essentially constant distance G from the array of cavities 11 .

[0089] In other words, the first trench has the same shape as the outline of the arrangement.

[0090] Throughout the description, the distance G represents the average distance. More specifically, the change in the distance between the first contour and the array of cavities can be observed.

[0091] The first trench 21 has a first depth p1 which is advantageously equal to the depth p.

[0092] Advantageously, steps (a1) and (a) are carried out simultaneously.

[0093] According to a preferred embodiment of the invention, the distance G is between one-fifth b (b / 5) and 5b (5×b), advantageously between half b (0.5×b) and 2b (2×b), and more advantageously between 0.9×b and 1.1×b.

[0094] The method according to the invention also includes a step (b) of forming a membrane 19 sealing each cavity 11 .

[0095] Step (b) of forming the membrane 19 comprises in particular transferring an encapsulation film 16 onto the front surface 10a of the support substrate 10 and onto the first trenches 21 (FIGS. 7b, 7c, 8a, 8b and 8c).

[0096] More specifically, the transferring includes assembling the sealing surface 16a of the sealing film 16 with the front surface 10a.

[0097] In other words, the sealing film 16 seals the first trench 21 and the cavity 11 .

[0098] The membrane 19 is therefore suspended above the cavity 11 .

[0099] The encapsulation film 16 may comprise a semiconductor material, and advantageously the semiconductor material comprises at least one element selected from silicon, germanium, a silicon and germanium alloy, indium phosphide, a III-V semiconductor arsenide, a III-V semiconductor phosphide, or a III-V semiconductor nitride, silicon carbide.

[0100] The sealing film 16 may comprise a metallic material, which advantageously comprises at least an element selected from aluminum, copper, titanium, tungsten, tungsten silicide, and gold.

[0101] The sealing film 16 may comprise an insulating material, which advantageously comprises at least an element selected from silicon dioxide, silicon nitride.

[0102] The encapsulation film 16 comprises a piezoelectric material, which advantageously comprises at least an element selected from lithium tantalate, lithium niobate, aluminum nitride, zinc oxide, zinc and lead tantalate.

[0103] The encapsulation film 16 may also include a stack of layers, in particular a stack of LTO and Si.

[0104] Transferring the sealing film may include, in particular, a step (b1) of bonding a substrate, called donor substrate 17, to the front surface 10a, and a step (b2) of removing a first part of the donor substrate 17, called handle substrate 17a, so as to retain only a second part of the substrate that forms the sealing film 16 (Figures 7b and 8a).

[0105] It is understood that the bonding step (b1) may involve molecular (or direct) bonding or thermocompression bonding or eutectic bonding.

[0106] The bonding step (b1) can also be carried out in a vacuum or a controlled atmosphere, in particular to apply a predetermined gas and pressure to the cavity 11 sealed using a sealing film 16.

[0107] More generally, any method of attachment known to those skilled in the art can be used within the scope of the present invention.

[0108] According to a first alternative of this first embodiment, step (b2) may comprise a thinning step (FIGS. 7a to 7c).

[0109] The thinning step may include wet etching, dry etching or mechanical abrasion (grinding), among others.

[0110] For example, a handle substrate 17a comprising silicon can be etched using a wet process with KOH or TMAH solutions.

[0111] Particularly advantageously, within the scope of this first embodiment, the donor substrate 17 comprises an intermediate layer 17 c interposed between the handle substrate 17 a and the sealing film 16 .

[0112] The intermediate layer 17c has in particular a selective etching surface with respect to the sealing film 16. It is therefore possible to consider the thickness of the sealing film 16 to be less than 20 μm or equal to 10 μm, for example 5 μm.

[0113] According to this alternative, the donor substrate 17 can in particular be a silicon-on-insulator (SOI) substrate, with the insulating layer being the intermediate layer. The silicon layer of the SOI substrate is advantageously highly doped. The barrier layer can be etched using an abrasive or selective chemical etching step.

[0114] According to a second alternative to the first embodiment, step (b1) can be preceded by a step of forming embrittled areas 17d delimiting the sealing film in the donor substrate, which are areas prone to fracture of the donor substrate 17 during step (b2), in particular under the influence of thermal treatment and / or mechanical action (Figures 8a to 8c).

[0115] The embrittled region 17d can be an amorphized region or an implanted region, in particular a region implanted with hydrogen atoms.

[0116] Regardless of the alternative embodiment considered, step (a1) may also comprise the formation of at least a second contour 31. The second contour, like the first contour 21, may in particular comprise a second trench which is advantageously continuous.

[0117] The second trench 31 advantageously forms, for example, a closed contour around the first trench 21 at all points essentially at a constant distance from the first trench 21 (FIGS. 10a and 10b).

[0118] The depth of at least the second trench 31, referred to as the second depth p2, may be equal to the depth p.

[0119] The first trench 21 and at least the second trench 31 may be connected by one or more interconnecting channels 40. In particular, the one or more interconnecting channels may connect two adjacent corners of the first trench and the second trench, respectively (FIG. 10b).

[0120] Particularly advantageously, the sealing film transferred during step (b) also seals at least the second trench.

[0121] Taking into account the first trench 21 and optionally at least the second trench 31, it is possible to reduce the non-uniformity in terms of film deformation that is likely to be observed between the center and the edge of the matrix arrangement.

[0122] In particular, the inventors have demonstrated that the distance G directly affects the uniformity of the deflection of the membrane circumscribed by the first contour 21. In particular, after sealing the cavity, species are more likely to diffuse at the bonding interface, more specifically during thermal treatment. In this respect, the cavity can function as a reservoir. Furthermore, the larger the bonding surface area surrounding the cavity, the greater the deformation of the transferred membrane. In other words, the distance G can be determined according to integration constraints (such as subsequent contact), the distance b separating the cavities of the array, and the desired uniformity. Thus, a distance G close to b will allow for better uniformity of the membrane deformation. On the other hand, considering that the distance G is greater than b, there is little or no beneficial effect. Figure 22 illustrates this perfectly. The latter is a graph of the average membrane deformation (in nm on the vertical axis) as a function of the spacing b. In this regard, it is noteworthy that the deformation increases with the spacing b.

[0123] Furthermore, Figures 11a and 11b are images obtained using an optical microscope, which make it possible to observe the effect of the first trenches 21 on the deformation of the membrane in relation to the deformation observed in the absence of the membrane.

[0124] A comparison of these figures clearly reveals the beneficial effect of the first trenches 21 on the non-uniformity of the deformation of the membrane. In particular, the first trenches make it possible to reduce the non-uniformity of the deformation of the membrane.

[0125] Leading to the same conclusion, Figures 12a and 12b represent measurements using optical interferometry of the regions associated with Figures 11a and 11b, respectively. Notably, the amplitude of membrane deformation is much more uniform from one membrane to another in Figure 12b.

[0126] The method according to the invention may also comprise a step (c), performed after step (b), of removing the portion of the sealing film overlapping the first trench and / or at least the second trench.

[0127] In other words, after step (c), the sealing film is retained over the cavity and removed in the first trench and / or at least the second trench.

[0128] This removal step (c) may involve wet etching or dry etching.

[0129] Figures 13a, 13b, 14a, 14b and 15 show various steps of a method for sealing a cavity according to a first aspect of a second embodiment of the invention.

[0130] The second manufacturing embodiment differs in this respect from the first embodiment in that a first contour 21, and if considered, a second contour 31, is formed in the sealing film 16. In particular, the first contour 21 will hereinafter be limited to a first trench in this disclosure.

[0131] A first aspect of this second embodiment is shown in FIGS. 13a, 13b, 14a, 14b and 15. FIG.

[0132] More specifically, the method shown in Figures 13a and 13b uses the terminology of the first alternative embodiment of the first embodiment, while the method shown in Figures 14a and 14b uses the terminology of the second alternative embodiment of the first embodiment.

[0133] 13a and 14a show the donor substrate 17 on the surface (sealing surface 16a) where the first contour 21 is formed.

[0134] According to this alternative embodiment, the first contour 21 has a first depth that is less than the thickness of the sealing film.

[0135] The support substrate 10 in which the array of cavities 11 is formed is then assembled with a donor substrate 17 (Figures 13b and 14b).

[0136] After step (b) shown in FIG. 15, the array of cavities 11 is circumscribed by first trenches 21 .

[0137] Regardless of the envisaged embodiment or alternative embodiment, "circumscribing" means that the protrusion of the first trench on the front surface surrounds the array of cavities.

[0138] The encapsulation film 16 can be thinned to expose the first trenches 21 .

[0139] A second alternative to this second embodiment is shown in FIGS. 16a, 16b, 17a, 17b and 18. FIG.

[0140] According to this second alternative embodiment, the first trenches 21 have a depth greater than the thickness of the sealing film, so that after the transferring step, said first trenches 21 are exposed to the external environment (FIG. 21).

[0141] The method shown in Figures 16a and 16b uses the terminology of the first alternative embodiment of the first embodiment, while the method shown in Figures 17a and 17b uses the terminology of the second alternative embodiment of the first embodiment.

[0142] 16a and 17a show the donor substrate 17 on the surface (sealing surface 16a) where the first contour 21 is formed.

[0143] The support substrate 10 in which the array of cavities 11 is formed is then assembled with a donor substrate 17 (Figures 16b and 17b).

[0144] Figures 19a, 19b and 20 show various steps of a method for sealing a cavity according to a third aspect of the second embodiment of the invention.

[0145] According to the third embodiment, the depth of the first trench is greater than the thickness of the sealing film 16 .

[0146] In particular, the steps of the method shown in Figures 19a and 19b use the terminology of the method shown in Figures 16a and 16b. By considering the first trench and / or at least the second trench, it is possible to attenuate the deformation of the membrane that is likely to occur when transferring the sealing film, and therefore the non-uniformity of the deformation is also reduced.

[0147] The method according to the invention is advantageously used to manufacture MEMS, in particular MEMS comprising resonators each formed by a membrane / cavity pair.

[0148] Reducing the deformation sustained by the membrane leads to an increase in the combined quality factor of the resonator matrix array and therefore makes it possible to manufacture matrix arrays of capacitive ultrasonic transducers (cMUTs or capacitive micromachined ultrasonic transducers) that are much more sensitive than arrays known from the prior art.

[0149] The method according to the present invention can also be used to produce a removable substrate that can peel off a sealing layer that overlaps the cavity. The energy involved in the peel between the receiving substrate and the sealing film can be adjusted according to the matrix arrangement and dimensional characteristics of the cavity.

[0150] Regardless of the envisaged application, the method according to the invention makes it possible to carry out subsequent technological steps (photolithography, bonding, etching, film deposition steps, etc.).

[0151] Finally, it is understood that the first contour and / or the second contour may be formed on both the front surface 10a and the sealing surface 16a.

[0152] The present invention also relates to a device comprising a plurality of cavities 11 sealed using a plurality of membranes 19, This device is (a) a plurality of cavities 11 opening onto the front surface 10a of the support substrate 10 or onto the sealing surface of the sealing film, the cavities 11 advantageously being arranged in a matrix, having a depth p, a characteristic dimension a, and being spaced apart by a distance b; (b) a plurality of membranes 19 sealing each of the cavities 11 formed by a sealing film 16 assembled with the front surface 10a using its sealing surface; Equipped with The device includes a first contour of width L on one and / or the other of the front surface 10a and the sealing surface; The first contour advantageously comprises a continuous first trench 21, The plurality of cavities 11 are circumscribed by a first contour, said first contour being advantageously at an essentially constant distance G from the plurality of cavities, between one-fifth b (b / 5) and 5b (5×b), advantageously between half b (0.5×b) and 2b (2×b), more advantageously between 0.9×b and 1.1×b. [Explanation of symbols]

[0153] 10 Support substrate 10a front 11 Cavity 16 Sealing film 16a Sealing surface 17 Donor substrate 17a Handle board 17c middle class 17d Embrittlement area 19 membrane 21 First Trench 31 Second Trench 40 interconnection channels

Claims

1. A method for sealing a plurality of cavities (11) using a plurality of membranes (19), comprising: The method comprises: (a) forming a plurality of cavities (11) opening onto a front surface (10a) of a support substrate (10) or a sealing surface (16a) of a sealing film (16), the cavities (11) having a depth p, a characteristic dimension a, and being spaced apart by a distance b; (b) forming the plurality of membranes (19) by transferring the sealing film (16) overlapping the front surface (10a) and sealing each of the cavities (11), wherein the transferring includes assembling the front surface (10a) and the sealing surface (16a), and sealing each of the cavities (11); Including, The method comprises: selecting the distance G between one-fifth of b and 5b, or between half of b and 2b, or between 0.9*b and 1.1*b; and 10. A method for sealing a plurality of cavities (11), comprising a step (a1) performed before step (b) of forming a first contour on one and / or the other of the front surface (10a) and the sealing surface (16a), wherein the first contour comprises a first trench (21) having a width L and a first depth p1, and the forming of the first contour is performed such that after step (b), the plurality of cavities (11) are circumscribed by the first contour, and wherein the first contour is at a distance G from the plurality of cavities that is between one-fifth b and 5b, or between one-half b and 2b, or between 0.9 x b and 1.1 x b.

2. 2. The method of claim 1, wherein the width L is between one-fifth of a and 5a, or between one-half of a and 2a, or between 0.9*a and 1.1*a.

3. 3. A method according to claim 1 or 2, wherein the cavity (11) is square, circular or polygonal, in particular hexagonal.

4. 4. The method of claim 1, wherein the first contour is formed on the front surface, and wherein step (b) is followed by step (c) of partially removing the sealing film (16) to reveal the first contour, the partial removal retaining a portion of the sealing film (16) circumscribed by the first contour.

5. 5. The method according to claim 1, wherein the first contour is formed in the sealing surface and the first depth p1 is less than a thickness of the sealing film.

6. 6. The method according to claim 1, wherein step (a1) also comprises forming at least a second contour on one and / or the other of the front surface (10a) and the sealing surface (16a), comprising a second trench (31) around the first trench (21) at an essentially constant distance from the first contour.

7. The method of claim 6, wherein the first contour and the at least second contour are connected by one or more interconnecting channels (40).

8. 8. The method of claim 7, wherein the one or more interconnecting channels (40) connect two adjacent corners of the first contour and the second contour, respectively.

9. 9. The method according to claim 1, wherein the transferring step (b) comprises a step (b1) of bonding a donor substrate (17) with the support substrate (10), the donor substrate (17) comprising the sealing film (16) resting on a handle substrate (17a), followed by a step (b2) of removing the handle substrate (17a).

10. The method of claim 9 , wherein step (b2) comprises etching by mechanical and / or chemical abrasion.

11. 11. The method of claim 10, wherein the donor substrate (17) comprises an intermediate layer (17c) interposed between the handle substrate (17a) and the sealing film (16), the intermediate layer (17c) having etching selectivity with respect to the sealing film (16) and the handle substrate (17a).

12. 10. The method of claim 9, wherein the donor substrate (17) comprises an embrittlement zone (17d) delimiting the sealing film (16) and configured to break by application of mechanical stress and / or heat treatment.

13. 13. The method according to claim 12, wherein said embrittled zone (17d) is obtained by implantation of seeds.

14. 14. The method according to claim 9, wherein the first contour is formed in the sealing surface, and the first depth p1 is equal to or greater than a thickness of the sealing film, such that the first contour is exposed to an external environment after step (b).

15. 15. The method of any one of claims 1 to 14, wherein the encapsulation film (16) comprises a semiconductor material.

16. 16. The method of claim 15, wherein the semiconductor material comprises at least an element selected from silicon, germanium, a silicon and germanium alloy, indium phosphide, a III-V semiconductor arsenide, a III-V semiconductor phosphide, or a III-V semiconductor nitride, and silicon carbide.

17. 15. The method of any one of claims 1 to 14, wherein the sealing film (16) comprises a metallic material.

18. 18. The method of claim 17, wherein the metallic material comprises at least an element selected from aluminum, copper, titanium, tungsten, tungsten silicide, and gold.

19. 15. The method of any one of claims 1 to 14, wherein the sealing film (16) comprises an insulating material.

20. 20. The method of claim 19, wherein the insulating material comprises at least one member selected from silicon dioxide, silicon nitride.

21. 15. The method of any one of claims 1 to 14, wherein the sealing film (16) comprises a piezoelectric material.

22. 22. The method of claim 21, wherein the piezoelectric material comprises at least an element selected from lithium tantalate, lithium niobate, aluminum nitride, zinc oxide, zinc, and lead tantalate.

23. 23. The method according to any one of the preceding claims, wherein the first trench (21) is continuous.

24. 24. The method of claim 1, wherein the distance G is essentially constant.

25. 25. Use of the method according to any one of claims 1 to 24 for manufacturing a microelectromechanical system.

26. A device comprising a plurality of cavities (11) sealed using a plurality of membranes (19), the device comprising: (a) a plurality of cavities (11) opening onto a front surface (10a) of a support substrate (10) or a sealing surface of a sealing film, the cavities (11) having a depth p, a characteristic dimension a, and being spaced apart by a distance b; (b) a plurality of membranes (19) sealing each of the cavities (11) formed by the sealing film (16) assembled with the front surface (10a) using its sealing surface; Equipped with 1. A device comprising: a first contour of width L on one and / or the other of the front surface (10a) and the sealing surface, the first contour comprising a first trench (21), the plurality of cavities (11) being circumscribed by the first contour, the first contour being at a distance G from the plurality of cavities and being positioned such that the distance G is between one-fifth b and 5b, or between one-half b and 2b, or between 0.9 x b and 1.1 x b.

27. 27. The device of claim 26, wherein the first trench (21) is continuous.

28. 28. A device according to claim 26 or 27, wherein the distance G is essentially constant.

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