Method for manufacturing a structure comprising a plurality of buried cavities

Abstract

The present invention relates to a method for manufacturing a structure comprising a plurality of cavities confined between a thin layer and a carrier substrate, the method comprising the following steps: a) providing a donor substrate and a carrier substrate; b) implanting first light species into the donor substrate to form a uniform buried weakened plane which defines, together with the front face of the donor substrate, the thin layer to be transferred; c) locally implanting second species into the donor substrate so as to introduce these species into the uniform buried weakened plane only at second regions so as to form a functional buried weakened plane having: first regions comprising the first light species and not the second species, and the second regions comprising the first light species and the second species; d) forming a plurality of cavities that open onto a front face of the donor substrate or of the carrier substrate; e) joining, by direct bonding, the donor substrate to the carrier substrate, via their respective front faces, to form a bonded structure in which the cavities are vertically in line with either the first regions or the second regions of the functional buried weakened plane; f) applying a heat treatment to the bonded structure in order to cause spontaneous separation along the functional buried weakened plane and form the structure on the one hand and the rest of the donor substrate on the other hand.

Description

METHOD FOR MANUFACTURING A STRUCTURE COMPRISING A PLURALITY OF BURIED CAVITIES FIELD OF THE INVENTION

[0001] The present invention relates to the field of microelectronics and electromechanical microsystems. In particular, the present invention relates to a method for collectively manufacturing a plurality of buried cavities within a structure comprising a support substrate and a thin layer, the cavities being confined between the support substrate and the thin layer.

[0002] TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] MEMS devices (Microelectromechanical systems) are widely used for the manufacture of various sensors, targeting a multitude of applications: for example, pressure sensors, microphones, radiofrequency switches, electro-acoustic and ultrasonic transducers (for example pMUT "Piezoelectric Micromachined Ultrasonic Transducer"), etc. Many of these MEMS devices are based on a flexible membrane overhanging a cavity. In operation, the deflection of the membrane, linked to a physical parameter (for example the propagation of an acoustic wave for a pMUT), is converted into an electrical signal (or vice versa depending on whether the device is in receiver or transmitter mode).

[0004] There are several layer transfer methods for obtaining a structure comprising a thin layer (which will form the aforementioned membrane) overhanging a plurality of cavities. They are advantageously based on an assembly by direct bonding (i.e. without the addition of adhesive material) of a donor substrate and a support substrate, at their respective front faces. One or other of the substrates comprises cavities opening on the side of its front face, conventionally the support substrate. These cavities are sealed during the assembly step by molecular adhesion of the two substrates. A step of thinning the donor substrate gives rise to the transfer of a thin layer onto the support substrate. This thinning step can in particular be based on the Smart Cut process TMwhich implements a buried fragile plane, formed by implantation of light species in the donor substrate, which delimits, with a front face of the donor substrate, the thin layer to be transferred (typically of thickness less than 2μm). As is well known per se, the growth of microcracks in the buried fragile plane, by thermal and / or mechanical activation, leads to a separation along said plane which gives rise to the transfer of the thin layer onto the support substrate. The remainder of the donor substrate can be reused for a subsequent layer transfer.

[0005] Obtaining a high-quality thin-film transfer is nevertheless complex, due to the presence of cavities, above which there is no stiffening effect. The stiffening effect is here attributed to the presence of the front face of the support substrate in contact with the thin film.

[0006] Thus, the growth of microcracks in the buried fragile plane can generate, at the level of the cavities, blisters or even local exfoliations which irreversibly degrade the thin layer and correspond to transfer defects.

[0007] The transfer quality is all the more difficult to ensure as the size of the cavities is large. We typically aim for lateral cavity dimensions of the order of a few microns to several tens of microns, and this with a thin layer thickness remaining less than 2 μm.

[0008] SUBJECT OF THE INVENTION

[0009] The present invention proposes a method for collectively manufacturing a structure comprising a plurality of buried cavities, overhung by a high-quality thin layer, i.e. having a very low quantity of transfer defects. It is based on the formation of a buried fragile plane called functional, the characteristics and properties of which are different between first zones and second zones, which may or may not benefit from a stiffening effect: the objective is to decorrelate the maturation of microcracks in these two zones, to promote the quality of the layer transfer.

[0010] BRIEF DESCRIPTION OF THE INVENTION

[0011] The present invention relates to a method of manufacturing a structure comprising a plurality of cavities confined between a thin layer and a supporting substrate, the manufacturing method comprising the following steps:

[0012] (a) providing a donor substrate and a support substrate, each of the substrates having a front face and a back face;

[0013] b) the implantation of first light species in the donor substrate, to form a uniform buried fragile plane delimiting with the front face of the donor substrate, the thin layer to be transferred;

[0014] (c) localized implantation of second species into the donor substrate so as to introduce said second species into the uniform buried fragile plane only at second zones, to form a functional buried fragile plane having:

[0015] - first areas containing the first light species and not the second species, and

[0016] - the second zones, comprising the first light species and the second species;

[0017] d) forming a plurality of cavities opening at a front face of the donor substrate or the support substrate;

[0018] e) assembly by direct bonding of the donor substrate to the support substrate, at their respective front faces, to form a bonded structure in which the cavities are located directly above either the first zones or the second zones of the functional buried fragile plane;

[0019] f) applying a heat treatment to the bonded structure to cause spontaneous separation along the functional buried fragile plane and form on the one hand the structure and on the other hand the rest of the donor substrate.

[0020] According to advantageous characteristics of the invention, taken alone or in any feasible combination: the implantation of step c) is carried out in the presence of a mask, arranged on the front face of the donor substrate, directly above the first zones of the functional buried fragile plane; the formation of the cavities in step d) is carried out by local etching of the front face of the support substrate, for example by means of a mask arranged on said front face; after step c), step d) of forming the cavities comprises the etching of the front face of the donor substrate, directly above the second zones, the first zones being protected from etching by the mask;the method comprises, after step d) and after removal of the mask, a step c') of localized implantation of third species at the level of the front face of the donor substrate, the third species thus being implanted in the first zones of the functional buried fragile plane and in another buried plane located at a distance from and under the second zones of the functional buried fragile plane;step d) of forming the cavities is carried out before step c), and comprises:the application of a mask arranged on the front face of the donor substrate, directly above the second zones of the functional buried fragile plane intended to be formed in the subsequent step c), andthe etching of the front face of the donor substrate, directly above the first zones, the second zones being protected from etching by the mask;after step d) and after removal of the mask from the front face of the donor substrate, step c) of implantation is carried out, the second species thus being implanted in the second zones of the functional buried fragile plane and in another buried plane located at a distance from and under the first zones of the functional buried fragile plane; the second zones of the functional buried fragile plane are directly above the cavities, in the bonded structure, and the first light species are hydrogen ions or atoms, and the second species are helium ions or atoms;the first zones of the functional buried fragile plane are directly above the cavities in the bonded structure, the first light species are hydrogen ions or atoms, or helium ions or atoms, or hydrogen and helium ions or atoms, and the second species are silicon ions or atoms, capable of slowing down the growth kinetics of microcracks in the second zones of the functional buried fragile plane, compared to the growth kinetics of microcracks in the first zones; the assembly step e) involves at least one intermediate layer arranged on the donor substrate and / or on the support substrate, said intermediate layer having been deposited after one of steps a) to d).;

[0021] Other characteristics and advantages of the invention will emerge from the detailed description which follows with reference to the appended figures in which:

[0022] The present two structures produced according to the manufacturing method in accordance with the present invention;

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[0029] Figures 2a to 2f show steps of the manufacturing method according to a first embodiment of the present invention;

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[0036] Figures 3a to 3f show steps of the manufacturing method according to a second embodiment of the present invention;

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[0043] Figures 4a to 4f show steps of the manufacturing method according to a third embodiment of the present invention; note that step d) () occurs before step c) () in this third embodiment;

[0044] The present top view images of SOI structures with cavities not in accordance with the invention, obtained after the application of isothermal annealing at different temperatures;

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[0052] Figures 6a to 6f show steps of the manufacturing method according to a variant of the first embodiment of the present invention; note that an additional step c') is added after step d) in this variant, compared to the first embodiment illustrated in Figures 2a to 2f.

[0053] Some figures are schematic representations which, for the sake of readability, are not to scale. In particular, the thicknesses of the layers along the z axis are not to scale with respect to the lateral dimensions along the x and y axes. The same references in the figures may be used for elements of the same nature. DETAILED DESCRIPTION OF THE INVENTION

[0054] The invention relates to a method of manufacturing a structure 100 comprising a plurality of cavities 30 confined between a thin layer 10 and a support substrate 20, as illustrated in the. The structure 100 may optionally comprise at least one intermediate layer 50 between the thin layer 10 and the support substrate 20.

[0055] A first step a) of the manufacturing process consists of providing a donor substrate 11, from which the thin layer 10 will be transferred, and a support substrate 20 (,,,).

[0056] The donor substrate 11 and the support substrate 20 advantageously have the shape of a wafer, with a diameter typically greater than 100 mm, for example 150 mm, 200 mm or 300 mm, and each have a front face 11 a, 20 a and a rear face 11 b, 20 b. Their thickness is usually between 200 and 900 microns.

[0057] The donor substrate 11 may be formed from at least one material selected from silicon, germanium, III-V semiconductor compounds, silicon carbide, lithium tantalate, lithium niobate, or other material of interest for the intended application. The support substrate 20 may be formed from at least one material selected from silicon, germanium, III-V semiconductor compounds, silicon carbide, lithium tantalate, lithium niobate, a glass, a ceramic, or other material of interest for the intended application.

[0058] The following step b) of the method corresponds to an implantation of first light species in the donor substrate 11, across the entirety of its front face 11a (in other words, in full surface or "full plate"), so as to form a uniform buried fragile plane 12', delimiting with said front face 11a, the thin layer 10 to be transferred (,,,). The term uniform means here that the implantation characteristics are the same over the entire extent of the buried fragile plane 12'.

[0059] These light species can in particular be chosen from hydrogen and / or helium ions or atoms. As is well known with reference to the Smart Cut process TM, these first species, once implanted in the donor substrate 11, are capable of forming lenticular defects in the uniform buried fragile plane 12'; these defects are likely to develop in the form of microcracks, under thermal activation, by diffusion of the light species and coalescence of the lenticular defects. Let us recall that the lenticular defects are distributed in a thin layer buried in the donor substrate 11 and determined by the Gaussian implantation profile; this layer is called buried fragile plane for the sake of simplification.

[0060] The implantation energy defines the depth at which the uniform buried brittle plane 12' will be generated in the donor substrate 11. For a given implantation energy and a given material of the donor substrate 11, the implanted dose of light species is the essential parameter defining the kinetics of microcrack development, i.e. the kinetics of blistering (without stiffener) and fracture (in the presence of a stiffener).

[0061] The applicant has identified that, in order to obtain a high-quality thin layer transfer 10, in a structure 100 with cavities, the required characteristics and properties of the buried fragile plane are different depending on whether said plane is located directly above a region benefiting from a stiffening effect or directly above a cavity (therefore without a stiffening effect). In the regions benefiting from a stiffening effect, it appears advantageous for the fracture kinetics to be “slowed down”, so as to allow the use of relatively high temperatures during the heat treatment intended to cause spontaneous separation in the buried fragile plane, while maintaining controllable treatment times; a higher temperature also allows greater pressurization of the microcracks and promotes the continuity of the fracture wave.In areas not benefiting from a stiffening effect (along the cavities), it is advantageous that the development of microcracks, during the aforementioned heat treatment, leads to large blisters, without premature local exfoliation.

[0062] This objective is achieved by implementing the manufacturing method according to the invention which provides for producing a functional buried fragile plane 12 comprising first zones Z1 different from second zones Z2, in terms of doses and / or nature of the implanted species.

[0063] Step c) of the method corresponds to a localized implantation of second species in the donor substrate 11 so as to introduce said second species into the uniform buried fragile plane 12' only at the level of second zones Z2. This makes it possible to form the functional buried fragile plane 12 (,,,). The latter then has, in the plane (x,y) of the front face 11a:

[0064] - first Z1 zones comprising the first light species and not the second species, and

[0065] - the second zones Z2, comprising the first light species and the second species.

[0066] The second species may be of the same nature as the first species or of a different nature. The implantation energy used to introduce the second species is adjusted so that their implantation profile is substantially superimposed on the implantation profile of the first light species. Advantageously, the maxima of the implantation profiles of the first and second species are located at depths equal to + / -20%, even more advantageously to + / -10%.

[0067] Localized implantation can be obtained by different means. A first option, implemented in a first and a second embodiment of the invention (,), consists of using a mask (M), applied to the front face 11a of the donor substrate 11, so as to protect the first zones Z1 from implantation. Such a mask is conventionally formed using deposition, lithography and etching techniques. Another option, illustrated in the, with reference to a third embodiment of the invention, is to take advantage of a difference in relief at the level of the front face 11a, between the regions directly above the first zones Z1 and those directly above the second zones Z2, so as to localize the second species in the second zones Z2 of the functional buried fragile plane 12 and to introduce them at a distance and below the first zones of said plane 12, in another discontinuous buried plane 12''.The second species will then be able to participate in the characteristics and properties of the second zones Z2 but not (or in a very limited way) in those of the first zones Z1.

[0068] In a step d) of the method, a plurality of cavities 30 are formed at the front face 11a of the donor substrate 11 (1 er and 3 ème embodiments,,and) or that 20a of the support substrate 20 (2 ème embodiment,).

[0069] It is important to note that step d) can be carried out after step c) (1 er embodiment,,) or before step c) (3 ème embodiment,) or in parallel with step c) (2 eme embodiment,).

[0070] The formation of the cavities in one of the substrates is conventionally carried out by local etching of the front face 11a, 20a, for example by means of a mask (M, M') arranged on said front face 11a, 20a.

[0071] The depth of the cavities 30 can typically vary between 100nm and 100μm. Their shape, in the (x,y) plane of the front face 11a,20a of the substrate concerned 11,20, can be circular, square, rectangular or polygonal. The characteristic dimension(s) (or lateral dimension(s)) of a cavity 30 in the (x,y) plane, namely its diameter (for a circular shape) or its side (for a square shape) or its width and its length (for a rectangular shape), is (are) typically between 1μm and 500μm. The spacing between the cavities 30 can be between 1μm and a few hundred mm.

[0072] The 1 er and 3 èmeembodiments, which provide for the formation of the cavities 30 in the donor substrate 11 (,), have the advantage of requiring only one mask (M) for carrying out steps c) and d). These embodiments nevertheless limit the range of possible depths of the cavities, since the depth must remain less than the difference between the depth of the functional buried fragile plane 12 and the target thickness of the thin layer 10 to be transferred.

[0073] The 2nd ème embodiment provides for the formation of the cavities 30 in the support substrate 20 (). In this case, it is necessary that the mask M' used to define the position of the cavities 30 on said substrate 20 and the mask M used to define the position of the first and second zones Z1, Z2 allow the correspondence between cavities 30 and first or second zones Z1, Z2, during the subsequent assembly step.

[0074] The manufacturing method then comprises a step e) of assembly by direct bonding of the donor substrate 11 on the support substrate 20, at their respective front faces 11a, 20a, to form a bonded structure 90 (,,,). A bonding interface 40, free of adhesive material, is defined between the two assembled faces.

[0075] The cavities 30 are located directly above either the first zones Z1 or the second zones Z2 of the functional buried fragile plane 12, depending on the implementation methods.

[0076] The principle of direct bonding, well known in the state of the art, will not be described in detail here. Because it is based on molecular adhesion between assembled faces, a very good surface condition (cleanliness, low roughness, etc.) of the substrates 11,20 is required to obtain good assembly quality.

[0077] Prior to assembly, preparation of the donor substrates 11 and support 20 is usually carried out. For example, a conventional sequence used in microelectronics, particularly for silicon-based substrates, comprises ozone cleaning, SC1 type cleaning (“Standard Clean 1”) and SC2 type cleaning (“Standard Clean 2”), with interspersed rinsing. Activation of the surfaces to be assembled, for example by plasma, may also be carried out before contact, to promote high bonding energy between said surfaces.

[0078] Optionally, the donor substrate 11 and / or the support substrate 20 may comprise an intermediate layer 50, at least at their respective front faces 11a, 20a, to promote the bonding quality and the bonding energy of their interface, or for the needs of the application (,,,). This intermediate layer may in particular be formed from an insulating material, such as silicon oxide, silicon nitride, etc. In the particular case where the donor substrate 11 and the support substrate 20 are made of silicon, the structure 100 obtained at the end of the process is then an SOI (silicon on insulator) structure with buried cavities 30.

[0079] The intermediate layer 50, arranged on the donor substrate 11 and / or on the support substrate 20, can be formed by growth or deposition after one of steps a) to d) of the method.

[0080] The direct bonding of step e) can be carried out under ambient atmosphere or under controlled atmosphere (for example, in a low pressure enclosure).

[0081] The following step f) of the manufacturing method corresponds to the application of a heat treatment to the bonded structure 90 to cause spontaneous separation along the functional buried fragile plane 12 and to form on the one hand the structure 100 and on the other hand the remainder of the donor substrate 11' (,,,). The structure 100 comprises the thin layer 10, assembled to the support substrate 20, either directly or via an intermediate layer 50, along a bonding interface 40, and buried cavities 30.

[0082] As mentioned above, the applicant has identified that the quality of the transfer of the thin layer 10 from the donor substrate 11 onto the support substrate 20 was improved by applying higher separation temperatures. The present images of a portion of the surface of several SOI structures with cavities (not in accordance with the invention), after transfer, for different heat treatment temperatures between 350°C and 450°C (isothermal annealing). It is clearly apparent that the density of transfer defects (in black on the images) decreases with the increase in the heat treatment temperature of step f).

[0083] In the manufacturing method according to the invention, the functional buried fragile plane 12 is composed of two zones Z1, Z2 having distinct implantation characteristics, which make it possible to promote, on the one hand, transfer kinetics compatible with “high” temperatures (in the regions benefiting from the stiffening effect), and on the other hand, the formation of large blisters at these temperatures with, possibly, a minimum of local exfoliation (in the regions directly above the cavities 30, not benefiting from the stiffening effect).

[0084] According to an example of implementation, it is the second zones Z2 of the functional buried fragile plane 12 which are in line with the cavities 30 in the bonded structure 90.

[0085] In the particular case of a targeted SOI-type structure 100 with cavities, the first light species may be hydrogen ions or atoms, and the second species helium ions or atoms. In practice, the donor substrate 11 is therefore made of monocrystalline silicon, the support substrate 20 is made of silicon, and an intermediate layer 50 of silicon oxide (for example, 200 nm thick) is arranged in whole or in part on one and / or the other of the front faces 11a, 20a, before assembly. For example, the cavities 30 are made on the donor substrate 11, and have a depth of 100 nm, lateral dimensions of 40 μm and a spacing of 7 μm. The implantation energy of the first light species (hydrogen) is 140 keV, with a dose of 6 E 16 / cm 2 ; the implantation energy of the second species (helium) is 220 keV, with a dose of 2 E 16 / cm 2 .

[0086] The first Z1 zones of the functional buried fragile plane 12, which only contain hydrogen species, are directly above regions benefiting from a stiffening effect; the implantation characteristics in the first Z1 zones are here favorable to a transfer in the higher temperature ranges (typically greater than or equal to 450°C).

[0087] The second zones Z2 of the functional buried fragile plane 12, which comprise the first species (hydrogen) and the second species (helium), are directly above regions not benefiting from the stiffening effect (cavities 30); the implantation characteristics in the second zones Z2 are here favorable to the formation of large blisters, in the aforementioned “high” temperature ranges.

[0088] According to another example of implementation, it is the first zones Z1 of the functional buried fragile plane 12 which are arranged in line with the cavities 30 in the bonded structure 90.

[0089] In the particular case of a targeted structure 100 of the SOI type with cavities, the first light species may be hydrogen ions or atoms, or helium ions or atoms, or hydrogen and helium ions or atoms (step c) would then consist of a co-implantation, i.e. two successive implantations of these two light species). The second locally implanted species are ions or atoms capable of slowing down the growth kinetics of microcracks in the second zones Z2 of the functional buried fragile plane 12, compared to the growth kinetics of microcracks in the first zones Z1. These second species may for example be silicon ions or atoms which will damage the material of the donor substrate 11 to a level more or less close to amorphization and thus modify the growth kinetics of the microcracks.Second species of a different nature could of course be introduced to achieve this same objective.

[0090] In practice, the donor substrate 11 is made of monocrystalline silicon, the support substrate 20 is made of silicon, and an intermediate layer 50 of silicon oxide (for example, 200 nm thick) is arranged on the front face 20a, before assembly. For example, the cavities 30 are made in the donor substrate 11, and have a depth of 100 nm, lateral dimensions of 40 μm and a spacing of 7 μm. The implantation energy of the first light species (co-implanted hydrogen and helium) is 32 keV (H) and 52 keV (He), with respective doses of 1 E 16 / cm 2 and 1.5 E 16 / cm 2 ; the implantation energy of the second species (Si) is 360 keV, with a dose of 10 E 14 / cm 2 .

[0091] The first zones Z1 of the functional buried fragile plane 12, which only contain the first hydrogen and helium species, are directly above regions not benefiting from a stiffening effect (cavities 30); the implantation characteristics in the first zones Z1 are here favorable to the formation of large blisters with, possibly, limited local exfoliations, in the “high” temperature ranges desired for step f) of separation heat treatment.

[0092] The second zones Z2 of the functional buried fragile plane 12, which comprise the first species (hydrogen and helium) and the second species (Si), are directly above regions benefiting from the stiffening effect; the implantation characteristics in the second zones Z2 are here favorable to a transfer in the “high” temperature ranges (typically greater than or equal to 450°C).

[0093] Note that the manufacturing method may comprise, after step f), conventional finishing and / or smoothing steps (mechanical, mechano-chemical, chemical or thermal) of the free surface 10a of the thin layer 10, with the aim of achieving the crystalline and surface quality required for said thin layer 10 in the final structure 100.

[0094] According to a variant of the first embodiment of the invention, illustrated in Figures 6a to 6f, a step c') of localized implantation of third species at the level of the front face 11a of the donor substrate 11 can be carried out. This step c') can in particular occur after the step d) of forming the cavities 30 in the donor substrate 11, and after removal of the mask M ('). The third species are thus implanted in the first zones Z1 of the functional buried fragile plane 12 and in another discontinuous buried plane 12'' located at a distance from and under the second zones Z2 of the functional buried fragile plane 12. These third species participate in modifying the characteristics and properties of the first zones Z1 of the functional buried fragile plane 12, but do not affect or only slightly affect those of the second zones Z2.

[0095] After the transfer of the thin layer 10, the discontinuous buried plane 12'' is found in the rest of the donor substrate 11' ().

[0096] The present invention can be used for a wide range of MEMS or NEMS (“Nanoelectromechanical systems”) devices, or for any other application taking advantage of a thin layer 10 arranged locally on a cavity 30, within a structure 100. As already mentioned in this description, an SOI (Silicon on Insulator) substrate with buried cavities is a known example of such a structure 100.

[0097] The invention is not limited to the embodiments described and variant embodiments may be made without departing from the scope of the invention as defined by the claims.

Claims

A method of manufacturing a structure (100) comprising a plurality of cavities (30) confined between a thin layer (10) and a support substrate (20), the manufacturing method comprising the following steps: a) providing a donor substrate (11) and a support substrate (20), each of the substrates (11, 20) having a front face (11a, 20a) and a rear face (11b, 20b); b) implanting first light species in the donor substrate (11), to form a uniform buried fragile plane (12') delimiting with the front face (11a) of the donor substrate (11), the thin layer (10) to be transferred;c) the localized implantation of second species in the donor substrate (11) so as to introduce said second species into the uniform buried fragile plane (12') only at the level of second zones (Z2), to form a functional buried fragile plane (12) having:- first zones (Z1) comprising the first light species and not the second species, and- the second zones (Z2), comprising the first light species and the second species;d) the formation of a plurality of cavities (30) opening at a front face (11a, 20a) of the donor substrate (11) or of the support substrate (20);e) the assembly by direct bonding of the donor substrate (11) on the support substrate (20), at their respective front faces (11a, 20a), to form a bonded structure (90) in which the cavities (30) are located directly above either the first zones (Z1) or the second zones (Z2) of the functional buried fragile plan (12);f) applying a heat treatment to the bonded structure (90) to cause spontaneous separation along the functional buried fragile plane (12) and form on the one hand the structure (100) and on the other hand the remainder of the donor substrate (11').; Manufacturing method according to claim 1, in which the implantation of step c) is carried out in the presence of a mask (M), arranged on the front face (11a) of the donor substrate (11), directly above the first zones (Z1) of the functional buried fragile plane (12). Manufacturing method according to claim 2, in which the formation of the cavities (30) in step d) is carried out by local etching of the front face (20a) of the support substrate (20), for example by means of a mask (M') arranged on said front face (20a). Manufacturing method according to claim 2, in which, after step c), step d) of forming the cavities (30) comprises etching the front face (11a) of the donor substrate (11), directly above the second zones (Z2), the first zones (Z1) being protected from etching by the mask (M). Manufacturing method according to claim 4, comprising, after step d) and after removal of the mask (M), a step c') of localized implantation of third species at the level of the front face (11a) of the donor substrate (11), the third species thus being implanted in the first zones (Z1) of the functional buried fragile plane (12) and in another buried plane (12'') located at a distance from and under the second zones (Z2) of the functional buried fragile plane (12). Manufacturing method according to claim 1, in which step d) of forming the cavities (30) is carried out before step c), and comprises: - the application of a mask (M) arranged on the front face (11a) of the donor substrate (11), in line with the second zones (Z2) of the functional buried fragile plane (12) intended to be formed in the subsequent step c), and - the etching of the front face (11a) of the donor substrate (11), in line with the first zones (Z1), the second zones (Z2) being protected from etching by the mask (M). Manufacturing method according to claim 6, in which after step d) and after removal of the mask (M) from the front face (11a) of the donor substrate (11), step c) of implantation is carried out, the second species thus being implanted in the second zones of the functional buried fragile plane (12) and in another buried plane (12'') located at a distance from and under the first zones (Z1) of the functional buried fragile plane (12). Manufacturing method according to one of claims 1 to 5, in which: - the second zones (Z2) of the functional buried fragile plane (12) are directly above the cavities (30), in the bonded structure (90), and - the first light species are hydrogen ions or atoms, and the second species are helium ions or atoms. Manufacturing method according to one of claims 1, 2, 3, 6 and 7, in which:- the first zones (Z1) of the functional buried fragile plane (12) are in line with the cavities (30) in the bonded structure (90),- the first light species are hydrogen ions or atoms, or helium ions or atoms, or hydrogen and helium ions or atoms, and- the second species are silicon ions or atoms, capable of slowing down the growth kinetics of microcracks in the second zones (Z2) of the functional buried fragile plane (12), compared to the growth kinetics of microcracks in the first zones (Z1). Manufacturing method according to one of claims 1 to 9, in which the assembly step e) involves at least one intermediate layer (50) arranged on the donor substrate (11) and / or on the support substrate (20), said intermediate layer (50) having been deposited after one of steps a) to d).

Images