FR3039926A1 - METHOD FOR ASSEMBLING ELECTRONIC DEVICES - Google Patents

Abstract

The present invention relates to a method of assembling a first electronic device comprising a first substrate (100) and a second electronic device comprising a second substrate (500), the method comprising: a step of forming at least one pattern (201, 202) on a first face (101) of the first substrate (100), a step of forming at least one pattern (601, 602) on a first face (501) of the second substrate (500), a relative positioning step of the first and second substrates (100, 500) comprising a mapping of the at least one pattern (201, 202) of the first substrate (100) and the at least one pattern (601, 602) of the second substrate ( 500), a step of joining the first substrate (100) to the second substrate (500). Prior to the positioning step and the securing step, at least one trench (151, 152) is formed in the thickness of the first substrate (100) configured to form a membrane (801, 802) between the first face (101) of the first substrate (100) and a second face (102) of the first substrate (100), opposite the first face (101), the pattern (201, 202) being carried by the membrane.

Description

FIELD OF THE INVENTION

The present invention relates to three-dimensional 3D integration for electronic devices and in particular microelectronic devices, the term microelectronics including nanotechnologies. The invention more particularly relates to an improved method of assembling electronic devices.

BACKGROUND

The race for miniaturization has physical limitations that challenge the planar approach used to this day. Indeed, the small dimensions of the new technological nodes reveal previously insignificant parasitic effects that could degrade the performance of the electronic components.

Among the processes under study, there is a three-dimensional architecture called "3D integration", which consists in vertically stacking electronic components, superimposing chips formed for example on substrates and / or plates on each other and by establishing short vertical electrical connections between these components, directly through the different layers. The concept of 3D integration allows devices to be realized with a multitude of functionalities as well as drastically reducing the lengths of the interconnections, thus increasing the communication speeds between the different components. 3D integration also requires control over the electrical connections between the different chips stacked vertically. It faces many challenges, including the complexity of design.

Several technological steps are to be mastered in order to achieve a 3D three-dimensional structure and among them: the assembly of the different substrates (or chips) by a bonding process, the thinning of the substrates once assembled and the realization of the vertical connections passing through the substrate to allow the electrical connection (also called "TSV" for "Through Silicon Vias" when these substrates are silicon). Moreover, the two types of connectors generally used to bring the signals to the inputs and outputs of a circuit are the external wiring (in English "wire bonding") and the return of flip chips (in English "flip chip"). The stacking of components in a 3D device can be done in several ways: plate to plate (acronym "W2W" for "Wafer To Wafer"), plate chip (acronym "D2W" in English for "Die To Wafer" ), or smart chip (acronym "D2D" for "Die To Die"). The plate-to-plate stack has the fastest approach to achieve because it allows you to assemble a large number of components simultaneously. The step of aligning the devices to be stacked is an essential step to obtain high densities of interconnections. The dimensions being of the order of a few microns, this implies an alignment to the same accuracy. Complementary alignment marks are required on each face to be glued. First, the optical alignment of these marks is done in dedicated equipment. The bonding is then carried out by contacting the plates, followed by light pressure and localized at a central point of the plate. Systems known as "verniers" allow the reading of the alignment after gluing. Once the collage is made, the marks are found at the gluing interface; their reading is then done using an infrared microscope. By integrating alignment marks on the devices, it is thus possible to measure the alignment at several points of the plate so as to create a mapping of the alignment at any point of the plate.

To achieve the alignment, a first solution is to introduce between the plates to be assembled an imaging system which, coupled with an image analysis system, will allow the alignment of the marks. The problem of this solution is that the alignment is achieved because of the presence of the imaging system while the plates to be assembled are very far from each other which limits the accuracy of the alignment.

Another solution known under the name Smart view alignment and developed by the company EVG provides for aligning the substrates to move them laterally relative to each other, over great distances (for example according to the diameter of the plate) and following at least one of the three directions (x, y, z), with increased precision to be able to put them facing each other, before gluing. The disadvantage of this method is that any displacement error inevitably leads to an error in the alignment of the plates.

The present invention solves all or at least some of the disadvantages of current techniques by proposing an alternative embodiment method.

SUMMARY OF THE INVENTION

One aspect of the invention relates to a method of assembling a first electronic device comprising a first substrate and a second electronic device comprising a second substrate, the method comprising a step of forming at least one pattern on a first face of the first substrate, a step of forming at least one pattern on a first face of the second substrate, a step of relative positioning of the first and second substrates comprising a mapping of the at least one pattern of the first substrate and the at least one pattern of the second substrate, a step of joining the first substrate to the second substrate. Advantageously, prior to the positioning step and the securing step, at least one trench is produced in the thickness of the first substrate configured to form a membrane between the first face of the first substrate and a second face of the first substrate, opposed to the first face, the pattern of the first substrate being carried by the membrane.

Advantageously, the positioning step comprises detecting the mapping of the at least one pattern of the first substrate and the at least one pattern of the second substrate by optical transmission through the membrane. Particularly advantageously, the detection can be carried out through any type of substrate, regardless of its opacity and its overall thickness, provided that the membrane is adapted in thickness. The invention also relates to an electronic device comprising a first substrate and at least one pattern made on a first face of the first substrate, characterized in that it comprises at least one trench in the thickness of the first substrate configured to form a membrane between the first face of the first substrate and a second face of the first substrate opposite to the first face, the pattern being carried by the membrane. The invention relates to a system comprising a first and a second electronic device according to the present invention wherein the at least one pattern of the first substrate is in correspondence with the at least one pattern of the second substrate.

A technical effect produced by the present invention is to improve the alignment accuracy of electronic devices formed on substrates. Particularly advantageously, the device according to the present invention makes it possible to reduce the distance separating two substrates during the alignment step prior to the step of bonding said plates and thereby to minimize the errors related to the displacements of the substrates during the gluing step. The invention advantageously allows the use of light transmission positioning techniques through the substrates of the devices to be assembled, even if they are made of materials with high opacity, such as silicon, and / or with thicknesses substrates for which these materials are opaque, in the spectrum of visible light in particular.

BRIEF INTRODUCTION OF FIGURES

The objects, objects, as well as the features and advantages of the invention will emerge more clearly from the detailed description of an embodiment of the latter, which is illustrated by the following accompanying drawings, in which: FIG. a first electronic device comprising a first substrate. FIG. 2 illustrates the formation of a first pattern and a second pattern from a first face of the first substrate. FIG. 3 illustrates the formation of a first trench and a second trench from a second face of the first substrate. FIG. 4 illustrates the formation of a layer from the first face of the first substrate. FIG. 5 illustrates the step of relative positioning of the first device comprising a first substrate on a second device comprising a second substrate. - Figure 6 illustrates the step of securing the patterns of the first electronic device with patterns of a second electronic device. FIG. 7 illustrates the step of checking the alignment after gluing. FIG. 8 illustrates an embodiment where trenches are formed on both the first substrate and the second substrate. FIGS. 9A and 9B illustrate, by way of examples, the transmission obtained for different membrane thicknesses w depending on the wavelength for silicon-based membranes (FIG. 9A) and for nitride-based membranes of silicon (Figure 9B). FIGS. 10A and 10B illustrate the deformation of a membrane (in nanometers) as a function of the thickness h of the membrane. FIG. 10A illustrates the case of a silicon-based membrane for a membrane size of between 10 and 500 microns on a side. FIG. 10B illustrates the case of a silicon nitride membrane for a membrane size of between 10 and 500 microns on a side.

The drawings are given by way of examples and are not limiting of the invention. They constitute schematic representations of principle intended to facilitate the understanding of the invention and are not necessarily at the scale of practical applications. In particular, the relative thicknesses of the different layers and substrates may not be representative of reality. This is the case for the marks produced by the alignment patterns.

DETAILED DESCRIPTION

Before beginning a detailed review of embodiments of the invention, are set forth below optional features that may optionally be used in any combination or alternatively: - is made on the first substrate a first pattern and a second pattern positioned on a membrane, respectively, of a first trench and a second trench of the first substrate. Advantageously, the presence of at least two alignment patterns ensures better accuracy in alignment. - Prior to the positioning step and the step of securing the first substrate on the second substrate, at least one trench is produced in the thickness of the second substrate configured to form a membrane between a first face of the second substrate and a substrate. second face of the second substrate, opposite to the first face, the pattern of the second substrate being carried by the membrane. Advantageously, the presence of membranes carrying the alignment patterns on each of the first and second substrates allows optimized optical transmission through both the first substrate and the second substrate. - On the second substrate is produced a first pattern and a second pattern positioned on a membrane, respectively, of a first trench and a second trench of the second substrate. The step of joining the first substrate to the second substrate comprises direct bonding. Advantageously, direct bonding allows bonding between plates and / or chips that do not require bonding material, heating or high pressure. The step of joining is performed from the first faces of the first and second substrates. According to a preferred embodiment, said first faces carry the alignment patterns. At least one membrane is based on silicon. Advantageously, the invention applies to any type of substrate, even the substrates leaving very little, if any, light. - After the step of securing the first substrate on the second substrate, a step of controlling the matching of the at least one pattern of the first substrate and the at least one pattern of the second substrate by optical transmission. Once the first and second substrates are joined together, an alignment check can advantageously be performed through said first and second substrates. - The at least one trench in the first substrate is made from a second face, opposite to the first face, of the first substrate. - The electronic device comprises a first pattern and a second pattern positioned each carried respectively by a first trench and a second trench of the first substrate. - The membrane of the first substrate is based on silicon. The at least one membrane of the first substrate has a thickness of less than 10 microns, typically between 1 and 5 microns. In a particularly advantageous manner, the process according to the invention makes it possible to produce relatively thin membranes so that the optical transmission can be made through said membranes carrying the alignment patterns. The invention relates to the assembly of electronic devices, preferably microelectronic devices. According to the invention, the term "microelectronic device" is understood to mean a device comprising elements of micron and / or nanometric dimensions. The following method has the preferred aim of producing a (micro) electronic device with reference to FIGS. 1 to 8. Preferably, a device, a chip or a plate (more commonly referred to as "wafer") comprising at least one chip.

FIG. 1 illustrates a first electronic device comprising a first substrate 100. The first substrate 100 is preferably in the form of a plate, but may also be in the form of a panel. In a particularly advantageous manner, the first substrate 100 has a thickness of between 100 microns and 1 millimeter. According to one embodiment, the first substrate 100 comprises a plurality of layers. The first substrate 100 comprises a first face 101 and a second face 102, opposite to the first face 101. Preferably, the first substrate 100 is made of a non-conductive or low-conductive material.

The first substrate 100 is preferably formed of a silicon-based material (eg, polycrystalline silicon). The first substrate 100 may also be, in whole or in part, of poly-silicon. Particularly advantageously, the present invention applies to any type of substrate regardless of the transparency or the original opacity of said substrate. Thus, a silicon-based substrate, known to be relatively opaque and thus allowing to pass through the spokes, can be advantageously used.

FIG. 2 illustrates a particular embodiment where a first pattern 201 and a second pattern 202 are formed on a first face 101 of the first substrate 100. The first and second patterns 201, 202 advantageously serve as alignment marks. .

These patterns 201, 202 or alignment marks can be of any kind, for example crosses, bars or verniers as opposite. These patterns 201, 202 are made by standard means of microelectronics (photolithography, etching, etc.) in general during the method of producing components made on a plate. The material (or the absence of material) in which these patterns 201, 202 are made must have an optical difference (absorption difference, transmission, etc.) with the surrounding material (here the membrane) so as to induce a contrast that can be detected at the imaging system used for alignment.

According to a preferred embodiment, the first and second patterns 201, 202 are produced from the first face 101 of the first substrate 100 by a lithography step, followed by an etching step. The patterns 201, 202 may, in one example, be formed in the first substrate 100. In another embodiment, the patterns 201, 202 are formed in one or more of the layers formed on the first substrate 100. The patterns 201, 202 may according to one example being formed protruding from the surface of the first substrate 100. In another example, the patterns 201,202 can be printed in the first substrate 100. The gap between the first pattern 201 and the second pattern 202 of the first substrate 100 is preferably between a few microns and the diameter of the substrate 100. In general, these units 201, 202 are positioned at the edge of the substrate 100 and, preferably, diametrically opposed so as to ensure better accuracy of the alignment.

FIG. 3 illustrates a step of forming a first trench 151 and a second trench 152 from the second face 102, opposite to the first face 101, of the first substrate 100. The first trench 151 and the second trench 152 first substrate 100 is preferably formed by a lithography step, followed by a dry or wet etching step. Advantageously, the first and second trenches 151, 152 of the first substrate 100 are configured to align with the patterns 201, 202 formed from the first face 101 of the first substrate 100. The first and second trenches 151, 152 are made so as to be positioned facing, respectively, the first and second patterns 201, 202 of the first substrate 100 in a projection according to the thickness of said first substrate 100. Preferably, the step of forming one at least among the first and second trenches 151, 152 of the first substrate 100 is achieved by partial removal of the first substrate 100. The trench 151, 152 made in the thickness of the first substrate 100 is configured to form a membrane 801, 802, corresponding to a zone of reduced thickness, between the first face 101 of the first substrate 100 and the second face 102 of the first substrate 100. The membrane 801,802 c advantageously comprises a thickness less than the thickness of the first substrate 100. The membrane 801, 802 represents a thinned area relative to the thickness of the first substrate 100. The membrane 801, 802 is formed for preferentially optical purposes.

The membrane 801, 802 is advantageously sufficiently rigid not to call into question the solidity of the first substrate 100 and therefore not to weaken said first substrate 100 following the formation of said membrane 801, 802. Advantageously, the shrinkage partial of the first substrate 100 is formed so that the bottom of each of the trenches 151, 152 forms a membrane 801, 802 separating the bottom of said trenches 151, 152 of the second face 102 of the first substrate 100. Particularly advantageously, the partial removal of the first substrate 100 is carried out until the membrane 801, 802 reaches a sufficiently small thickness to allow the wavelengths to pass in the visible range.

Advantageously, the section of the membranes 801, 802 will be greater than the dimensions of the alignment patterns 201, 202 which will be used for the alignment. Preferably, the minimum diameter of the membranes 801, 802 is equal to at least the size of the patterns 201, 202. Preferably, the section of the trenches 151, 152 will be greater than the section of the membranes 801, 802. The patterns 201, 202 are of preferably formed in the material constituting the membrane 801, 802 so as not to generate defects and deformations during the securing step. The patterns 201, 202 may also be made in a layer deposited on the membranes 801, 802 after their formation.

Preferably, at least two membranes 801, 802 provided with patterns 201, 202 are used to align a first substrate 100 with a second substrate 500. In this case, one will advantageously choose diametrically opposed patterns 201, 202 on the substrate 100. one embodiment, a plurality of patterns 201, 202 are produced so that at least one pattern 201, 202 is positioned on a chip of the first substrate 100. According to another embodiment, a plurality of patterns are realized. 201, 202 so that at each corner of a chip is positioned a pattern 201, 202.

The membranes 801, 802 may advantageously be made at the very beginning of the process on the substrate 100. According to this non-represented and non-limiting embodiment of the invention, the step of forming the first trench 151 and the second trench 152 is made from the second face 102, prior to the step of forming the first pattern 201 and the second pattern 202. The first pattern 201 and the second pattern 202 can then be made on the first face of the substrate 100, either on the second face of the substrate 100.

The membrane 801, 802 may advantageously be made of the same material as that of the first substrate 100, for example silicon. According to another embodiment where the first substrate 100 comprises a plurality of layers, the membrane 801, 802 may be made of a material forming one of the plurality of layers of the first substrate 100. According to a non-limiting example of the invention , the plurality of layers of the first substrate 100 may be formed by a first polycrystalline silicon layer on a second layer of silicon dioxide (SiO 2), in the case of a device of "Silicon on insulator" type.

FIG. 4 illustrates the formation of a first layer 300 on the first face 101 of the first substrate 100. The first layer 300 is advantageously conductive. Particularly advantageously, the first layer 300 preferably comprises copper or tungsten. The first layer 300 may, however, be any metal. The first layer 300 has a thickness according to the thickness of the first substrate 100, preferably less than 200 microns (for example 100 microns).

According to one embodiment, the first layer 300 formed from the first face 101 of the first substrate 100 comprises functional devices aligned with the first and second patterns 201, 202. According to one embodiment, the first layer 300 comprises a electrical connection member, in other words any type of member that can be put in electrical continuity. They are advantageously formed using lithography, etching, deposition and heat treatment techniques.

FIG. 5 illustrates the step of positioning the first device comprising the first substrate 100 relative to a second device comprising a second substrate 500. The second substrate 500 is preferably made of a non-conductive or low-conductive material. The second substrate 500 is preferably based on silicon (for example, polycrystalline silicon), polysilicon or other semiconductor material. Advantageously, the second substrate 500 is in the form of a plate or a panel. In a particularly advantageous manner, the second substrate 500 has a thickness of between 100 microns and 1 millimeter. Advantageously, a step is performed for forming a first pattern 601 and a second pattern 602 on a first face 501 of the second substrate 500. The first and second patterns 601, 602 advantageously serve as alignment marks. According to a preferred embodiment, the first and second patterns 601, 602 are produced from the first face 501 of the second substrate 100 by a lithography step, followed by an etching step. The patterns 601, 602 may, in one example, be formed in the second substrate 500. In another embodiment, the patterns 601, 602 are formed in one or more of the layers formed on the second substrate 500.

Particularly advantageously, the first and second patterns of the first substrate 100 have locations which coincide with, respectively, the first and second patterns 601, 602 of the second substrate 500 when the first faces 101, 501 of the first and second substrates 100, 500 are assembled. . The relative positioning step preferably comprises a step of matching the first and second patterns 201, 202 of the first substrate 100 with the first and second patterns 601, 602 of the second substrate 500. Mapping is understood to mean the co-operation of the projection, in a plane perpendicular to the thickness of the substrate 100, of the first pattern 201 of the first substrate 100 with the projection, in a plane perpendicular to the thickness of the substrate 100, of the first pattern 601 of the second substrate 500 so that said projections cooperate by overlapping or interleaving.

Particularly advantageously, detection is made of the mapping of the at least one pattern 201, 202 of the first substrate 100 and the at least one pattern 601, 602 of the second substrate 500 by optical transmission through the bottom of the trench 151. , 152. Optical transmission is understood to mean the transmission of information transported by light waves according to the principle of partial or total reflection. An optical transmission system has three essential components: a light source (the optical transmitter), a light-guiding transmission medium, and a light detector (the optical receiver). The optical transmission and reception means 901, 902 are positioned so as to emit and respectively receive a signal perpendicular to the thickness of the first substrate 100 and through each membrane 801, 802 of the first substrate 100. embodiment, at least a portion of the transmitted rays will be reflected through at least one membrane 801, 802. In another embodiment where the first substrate 100 comprises at least one membrane 801, 802 provided with a pattern and the second substrate 500 comprises a pattern without membrane 803, 804, then the optical transmission will be advantageously through the first substrate 100 provided with the membrane 801, 802. In this embodiment, the optical transmission and reception means 901, 902 are positioned to emit and respectively receive a signal perpendicular to the thickness of the first substrate 100 through the membrane 801, 802 of the first substrate 10 0.

The offset accuracy, during the alignment step of the first and second patterns 201, 202, 601, 602 of the first and second substrates 100, 500, is, for example, less than one micron. The diameter of each pattern 201, 202, 601, 602 of the first substrate 100 and the second substrate 500 is configured to compensate for an offset in the alignment of the first and second patterns 201, 202, 601, 602 of the first and second substrates. 100, 500. An alignment is preferably performed in at least one of the three directions (x, y, z) and in rotation, minimizing the distance between the first and second substrates 100, 500 in order to reduce the risks of misalignment during the subsequent securing step.

As illustrated in FIG. 6, at the end of the step of matching the first and second patterns 201, 202, 601, 602, first and second substrates 100, 500, a step of joining the first substrate 100 to the first second substrate 500 is made. According to a preferred embodiment, the step of joining is carried out from the first faces 101, 501 of the first and second substrates 100, 500. According to one embodiment, the step of joining is made from the second faces 102, 502 of the first and second substrates 100, 500. According to another embodiment, the step of joining is carried out from the first face 101 of the first substrate 100 and from the second face 502 of the second substrate 500. The first and second patterns 201, 202, 601, 602, first and second substrates 100, 500 are preferably made on the first faces of the first and second substrates 100, 500. According to another embodiment, the first and second substrates 100, 500. second patterns 201, 202, 601, 602, first and second substrates 100, 500 are made on one or the other of the first and second faces 101, 102, 501, 502 of the first and second substrates 100 , 500. The patterns 201, 202, 601, 602 are particularly advantageously configured so that, during the securing step, the patterns 201, 202 of the first substrate 100 are not brought into contact (direct) with the patterns 601, 602 of the second substrate 500. The patterns 201, 202, 601, 602 advantageously fit into each other to improve the alignment accuracy and allow the approximation of the plates. The spacing between the first pattern 201 of the first substrate 100 and the first pattern 601 of the second substrate 500 is preferably between 1 nm to 100 μm, and preferably between a few nanometers and a micron.

Advantageously, the second substrate 500 comprises a second layer 700. The second layer 700 formed in the second substrate 500 has a thickness, preferably less than 200 microns (for example 100 microns). In a particularly advantageous manner, the first substrate 100 is secured to the second substrate 500 from the first layer 300 of the first substrate 100 and the second layer 700 of the second substrate 500, by a bonding effect that provides mechanical bonding and advantageously produces continuity electric. According to one embodiment, the second layer 700 comprises an electrical connection member, in other words any type of member that can be put in electrical continuity.

Advantageously, the first layer 300 of the first substrate 100 and the second layer 700 of the second substrate 500 are aligned in such a way that the alignment of the first substrate 100 and the second substrate 500 creates at least one continuous electrical connection coming from the contacting. first and second layers 300, 700, respectively of the first and second substrates 100, 500.

Several types of bonding exist to achieve in a single step a mechanical assembly and a metal interconnection. Two main technologies coexist, in particular by the strong adhesion, the good electrical conduction and the high density of interconnections obtained. This is sealing by thermo-compression or direct bonding. Preferably, the present invention uses the direct bonding method in English allowing direct bonding between plates or between chips, requiring no bonding material, no need for significant heating or high pressure. This technology is based on molecular adhesion phenomena between the atoms of the two opposite surfaces. The bonding step is preferably followed by annealing. The annealing has the advantage of reinforcing the bonding forces between the first substrate 100 and the second substrate 500. In a particularly advantageous manner, according to an embodiment where a stack of a plurality of substrates is produced, the annealing step consolidation of the sealing between a first substrate 100 and a second substrate 500, can be done after each transfer of a first substrate on a second substrate and / or after the formation of the stack of the plurality of substrates 100, 500.

FIG. 7 illustrates the step of controlling the alignment performed preferably after the step of joining the first and second substrates 100, 500, by optical transmission and reception means 901, 902. These control means 901 , 902 are particularly advantageously used as optical cameras and detectors of an optical signal through the first and second membranes 801, 802 of the first substrate 100. Advantageously, this control makes it possible to verify the proper alignment and complementarity of the patterns 201, 202 positioned on the first substrate 100 with the patterns 601, 602 positioned on the second substrate 500. This control can be achieved either "in situ" (that is to say in the same equipment as that where was performed the gluing step), or in another equipment.

FIG. 8 illustrates an embodiment where at least first and second trenches 551, 552 have been formed from the second face 502 of the second substrate 500. Particularly advantageously, these trenches 551, 552 formed from the second substrate 500 coupled to the trenches 151, 152 formed from the first substrate 100 allow to align the patterns 201, 202, 601, 602 with a better accuracy. Advantageously, the first and second trenches 551, 552 of the second substrate 500 are formed according to the same method as that used during the formation of the first and second trenches 151, 152 of the first substrate 100. In this particular embodiment, use is made of preferably optical cameras as optical transmission means 901, 902 positioned opposite the second face 102 of the first substrate 100 to emit an optical signal through the first 801,803 and second 802, 804 membranes respectively of the first and second substrates 100, 500 and detectors as optical receiving means 801, 802 positioned opposite the second face 502 of the second substrate 500 to receive the optical signal emitted by said cameras 901, 902.

In a particularly advantageous manner, the thickness of the membrane 801, 802 should be sufficiently fine so that the contrast obtained between the low transmissive zones (generally corresponding to the alignment patterns 201, 202) and the more transmissive zones (generally around patterns 201, 202) is greater than the sensitivity of the image acquisition system. Those skilled in the art will know, by routine procedures, to determine the maximum thickness of membrane compatible with its image acquisition system. It will be possible for him to increase this contrast by using to make the patterns 201, 202 a highly absorbent material at the wavelength used or by increasing the optical transmission through the membrane.

FIGS. 9A and 9B illustrate, by way of example, the transmission obtained for different membrane thicknesses w as a function of the wavelength for silicon-based membranes (FIG. 9A) and for nitride-based membranes. silicon (Figure 9B).

The at least one membrane 801, 802 of the first substrate 100 is, for example, configured so as to let at least 50% of the rays in the visible spectrum. Particularly advantageously, the contrast is greater than the sensitivity of the acquisition system. By visible spectrum or optical spectrum is meant the part of the electromagnetic spectrum visible to the human eye, that is to say a representation of all the monochromatic components of the visible light. The membrane 801, 802 has, for example, a thickness preferably of less than 10 microns, typically between 1 and 5 microns. Advantageously, the membrane 801, 802 should be sufficiently rigid so that it does not deform under its own weight.

The deformed u (0) of a membrane (at its center, maximum deformation point) square, of thickness h and width L in a material whose Young's modulus is E, the fish coefficient is υ, and the volume mass is p is given by the following relation:

Figures 10A and 10B illustrate the deformation of a membrane (in nanometers) as a function of the thickness h of the membrane. FIG. 10A illustrates the case of a silicon-based membrane for a membrane size of between 10 and 500 microns on a side. FIG. 10B illustrates the case of a silicon nitride membrane for a membrane size of between 10 and 500 microns on a side. It can be seen that the deformation of the membrane is less than a few nanometers which will guarantee the quality of the alignment. It is therefore the optical transmission of the membrane that will be optimized.

The present invention is not limited to the previously described embodiments but extends to any embodiment within its spirit. The invention is also applicable to any type of mechanically autonomous microelectronic device. The term "mechanically autonomous device" means a self-supporting device that can be used independently of another device and is self-sufficient from a mechanical point of view.

The method may, in a preferred manner, be repeated until a stack of a plurality of substrates 100, 500 of whatever thickness is obtained and provided with membranes 801, 802, 803, 804 having patterns 201, 202, 601, 602. alignment for mechanical stability to be achieved. The alignment between the different substrates 100, 500 forming the stack will be through the membranes with patterns 201, 202, 601, 602 alignment. The alignment concept may, particularly advantageously, be extrapolated to a plurality of other substrates of any type, regardless of their opacity and thickness.

Claims (14)

A method of assembling a first electronic device comprising a first substrate (100) and a second electronic device comprising a second substrate (500), the method comprising: a step of forming at least one pattern ( 201, 202) on a first face (101) of the first substrate (100), - a step of forming at least one pattern (601, 602) on a first face (501) of the second substrate (500), - a relative positioning step of the first and second substrates (100, 500) comprising a mapping of the at least one pattern (201, 202) of the first substrate (100) and the at least one pattern (601.602) of the second substrate (500) a step of securing the first substrate (100) to the second substrate (500), characterized in that, prior to the positioning step and the securing step, at least one trench is made (151, 152 ) in the thickness of the first substrate (100) configured to forming a membrane (801, 802) between the first face (101) of the first substrate (100) and a second face (102) of the first substrate (100), opposite to the first face (101), the pattern (201, 202 ) of the first substrate (100) being carried by the membrane, and in that the positioning step comprises detecting the mapping of the at least one pattern (201, 202) of the first substrate (100) and the at least one a pattern (601, 602) of the second substrate (500) by optical transmission through the membrane (801, 802). 2. Method according to the preceding claim wherein there is produced on the first substrate (100) a first pattern (201) and a second pattern (202) positioned on a membrane (801, 802), respectively, of a first trench (151). ) and a second trench (152) of the first substrate (100). 3. Method according to any one of the preceding claims wherein, prior to the positioning step and the step of securing the first substrate (100) on the second substrate (500), at least one trench is produced (551 , 552) in the thickness of the second substrate (500) configured to form a membrane (803, 804) between a first face (501) of the second substrate (500) and a second face (502) of the second opposed substrate (500) at the first face (501), the pattern (601,602) of the second substrate (500) being carried by the membrane (803, 804). 4. Method according to the preceding claim wherein there is produced on the second substrate (500) a first pattern (201) and a second pattern (202) positioned on a membrane (803, 804), respectively, of a first trench (551). ) and a second trench (552) of the second substrate (500). 5. Method according to any one of the preceding claims wherein the step of securing the first substrate (100) on the second substrate (500) comprises a direct bonding. 6. Method according to any one of the preceding claims wherein the step of joining is effected from the first faces (101, 501) of the first and second substrates (100, 500). 7. Method according to any one of the preceding claims wherein at least one membrane (801, 802, 803, 804) is based on silicon. 8. Method according to any one of the preceding claims comprising, after the step of securing the first substrate (100) on the second substrate (500), a step of controlling the matching of the at least one pattern (201, 202) of the first substrate (100) and the at least one pattern (601,602) of the second substrate (500) by optical transmission. The method of any one of the preceding claims wherein the at least one trench (151, 152) in the first substrate (100) is made from a second face (102), opposite to the first face (101). ), the first substrate (100). An electronic device comprising a first substrate (100) and at least one pattern (201, 202) formed on a first face (101) of the first substrate (100), characterized in that it comprises at least one trench (151, 152) in the thickness of the first substrate (100) configured to form a membrane (801, 802) between the first face (101) of the first substrate (100) and a second face (102) of the first substrate (100) opposite the first face (101), the pattern (201, 202) being carried by the membrane (801, 802). 11. Device according to the preceding claim wherein the at least one membrane (801, 802) of the first substrate (100) has a thickness less than 10 microns. 12. Device according to any one of the two preceding claims comprising a first pattern (201) and a second pattern (202) positioned each carried respectively by a first trench (151) and a second trench (152) of the first substrate. (100). 13. Device according to any one of the three preceding claims wherein the membrane (801, 802) of the first substrate (100) is based on silicon. A system comprising first and second electronic devices according to any one of claims 10 to 13 wherein the at least one pattern (201, 202) of the first substrate (100) is in correspondence with the at least one pattern (601 602) of the second substrate (500).