Method for the eutectic bonding of two substrates

Abstract

The method comprises the following steps: a) providing a first substrate (111) covered by a first bead (121) comprising a first element, b) providing a second substrate (112) covered by a second bead (122) comprising a second element, c) bringing the first bead (121) and the second bead (122) into contact, and performing a heat treatment to form a eutectic phase combining the first element and the second element, whereby a bonding bead (123) based on a eutectic alloy is formed and the first substrate (111) is bonded to the second substrate (112), the formation of the eutectic phase being accompanied by the formation of runs (123'), at least one of either the first substrate (111) and / or the second substrate (112) being locally covered by a wettability layer (130), whereby, during step c), the runs (123') of eutectic alloy form on the wettability layer (130).

Description

[0001] PROCESS FOR EUTECTIC SEALING OF TWO SUBSTRATES

[0002] DESCRIPTION

[0003] TECHNICAL FIELD

[0004] The present invention relates to the general field of microelectronics and, more particularly, to that of the encapsulation (or 'packaging') of a microelectronic device such as a MEMS ("Micro-Electro-Mechanical Systems"), NEMS ("Nano-Electro-Mechanical Systems"), MOEMS ("Micro-Opto-Electro-Mechanical Systems"), or NOEMS ("Nano-Opto-Electro-Mechanical Systems") type microsystem, consisting of encapsulating, or enclosing, this device in a hermetic cavity whose atmosphere is controlled.

[0005] The invention relates to a method for hermetically sealing two substrates.

[0006] The invention also relates to a device obtained by such a method.

[0007] The invention finds applications in many industrial fields, for example in the automotive sector, mobile phones and even video game consoles.

[0008] The invention is particularly interesting since it allows the substrates to be hermetically sealed with a eutectic alloy while avoiding the risks of short circuits or mechanical blocking of the mobile structures.

[0009] STATE OF THE PRIOR ART

[0010] Microelectronic devices such as MEMS, NEMS, MOEMS or NOEMS are nanometric or micrometric sensors or actuators. They are manufactured using microelectronics processes.

[0011] The encapsulation of these microelectronic devices allows, on the one hand, to protect them from external elements (humidity, particulate pollution, reactive elements such as oxygen) and, on the other hand, to control the atmosphere (pressure, composition of the encapsulated gas, etc.) prevailing in the cavity in which these devices are encapsulated. The encapsulation pressure prevailing in the cavity is variable depending on the intended application and is, typically, between 10 -3 mbar and 1 bar.

[0012] Different types of sealing can be implemented for this encapsulation: thermo-compression, eutectic sealing, anodic sealing, etc.

[0013] Currently, eutectic sealing appears to be the most promising.

[0014] Typically, as shown in Figures 1A and 1B, in the eutectic sealing method, the constituents of the alloy are deposited separately on the faces of the substrates 11, 12 to be assembled. On the first substrate 11, a first bead 21 of material is formed. On the second substrate 12, a second bead 22 of material is formed (Figure 1A).

[0015] During sealing, the two substrates 11, 12 are brought into intimate contact and a temperature is applied to the entire system. Fusion occurs at the eutectic temperature if the relative composition of the two materials corresponds to the eutectic concentration. In the liquid phase, a homogeneous liquid composed of the two materials is present between the two faces. Then the solidification of the solder will give rise to the formation of a material composed of a demixing of the materials used to make the eutectic fusion within the limit of their respective solubility. This material will then be called eutectic material even if it is not formed by a single phase. This eutectic material is then between the two substrates 11, 12 and allows the mechanical closure of the interface to form the final assembly.

[0016] The eutectic material thus passes through a liquid state before solidifying and forming a hermetic bead 23 around the chips to be encapsulated (figure 1B).

[0017] However, the transition to the liquid phase can be accompanied by the flow of eutectic material outside the area of ​​the sealing bead (figure 2). These drips 23', which solidify, can cause possible mechanical blockages of the mobile structures, and / or generate short circuits between different areas of the device.

[0018] It is therefore necessary to control the leakage of liquid solder.

[0019] For example, in V. Lumineau's thesis (2018 "Study of the realization of MEMS sealing by the eutectic alloy Al-Ge"), it was proposed to form stops adjacent to the beads. These stops limit the approach of the two plates to be assembled and therefore the crushing of the Al-Ge bilayer. However, for this solution to work, it is necessary to put solid stops on each side of the bead at a certain distance. However, this solution cannot be applied to all devices because of the compactness constraints of the different structures for example.

[0020] STATEMENT OF THE INVENTION

[0021] An aim of the present invention is to propose a eutectic sealing method which overcomes the drawbacks of the prior art and makes it possible to hermetically seal two substrates, while avoiding the phenomena of short circuits and mechanical blocking.

[0022] For this purpose, the present invention proposes a method for eutectic sealing of two substrates comprising the following steps: a) providing a first substrate having a first face covered by a first bead of a first material, and optionally by one or more microelectronic devices, the first material comprising a first element, b) providing a second substrate having a first face covered by a second bead of a second material, and optionally by one or more microelectronic devices, the second material comprising a second element, capable of forming a eutectic alloy with the first element, c) bringing the first bead and the second bead into contact, and carrying out a heat treatment to form a eutectic phase alloying the first element of the first bead and the second element of the second bead,whereby a sealing bead based on the eutectic alloy is formed and the first substrate is sealed to the second substrate, the formation of the eutectic phase being accompanied by the formation of eutectic alloy drips.,

[0023] It is also possible to use a first cord comprising the first material and the second material, for example in the form of a multilayer, and / or a second cord comprising the first material and the second material, for example in the form of a multilayer.

[0024] It is thus possible to form a symmetrical configuration. It is also possible to form an asymmetrical configuration, for example, by having a first bead comprising the first material and a second bead comprising the second material on which a portion of the first material has been deposited. In this case, the first material on the first face of the first substrate is thinner to maintain the eutectic concentration before melting.

[0025] According to another embodiment, the asymmetric configuration is obtained by having a second bead comprising the second material and a first bead comprising the first material on which a portion of the second material has been deposited. In this case, the second material on the first face of the second substrate is thinner to maintain the eutectic concentration before melting.

[0026] It is possible to modify the distribution of materials on one of the two sides or on both sides.

[0027] Advantageously, a configuration leading to the formation of an atomic flux across the bonding interface will be chosen, i.e. an asymmetric configuration.

[0028] In this method, at least one of the first substrate and the second substrate is locally covered by a wettability layer, the contact angle of a drop of eutectic alloy on the wettability layer being at least 20° and preferably at least 40° lower, on the one hand, than the contact angle of eutectic alloy on the first face of the first substrate and, on the other hand, than the contact angle of eutectic alloy on the first face of the second substrate, whereby during step c), the drips of eutectic alloy will preferentially go onto the wettability layer.

[0029] The invention fundamentally differs from the prior art by the implementation of at least one zone of preferential wettability of the eutectic alloy facing the substrate. The eutectic material formed during step c) has better wettability on the wettability layer than on the faces of the first and second substrates.

[0030] Thus, instead of putting a "physical" barrier (like the stops in the prior art), we use a so-called "energetic" barrier with a face with high surface energy for the liquid metal and a wetting zone with lower surface energy. The liquid metal will wet this wetting zone as if it were falling into a potential well. By judiciously integrating a preferential wettability layer, the drips of eutectic material will be guided and maintained in a "safe" zone for the functionality of the chip.

[0031] For example, in the case of the eutectic alloy Al-Ge, the wettability of this alloy is better on a metallic face than on a dielectric face. Positioning a metallic wettability layer in contact with or near the location of the sealing bead helps to contain drips in the case of a substrate having a face made of a dielectric material.

[0032] In particular, a substrate will be chosen for which the eutectic alloy droplet contact angle is greater than or equal to 90°, preferably greater than or equal to 100°.

[0033] For example, a wettability layer will be chosen for which the eutectic alloy droplet contact angle is less than or equal to 70°, preferably less than or equal to 60° and even more preferably less than or equal to 40°.

[0034] With this sealing process, the molten metal alloy adheres to the faces of the substrates to be assembled and the drips are contained at the level of the wettability layer. The cavity thus sealed is hermetic and the assembly has good mechanical strength.

[0035] Advantageously, the wettability layer (also called wetting layer) is a metal layer. Preferably, the metal layer is made of a metal chosen from W, Ti, Al, Au and Cu.

[0036] According to another advantageous variant, the wettability layer is a layer of metal nitride, such as TiN, WN, AIN.

[0037] According to another advantageous variant the wettability layer is a semiconductor layer such as Si, Ge, SiC, AsGa, InP.

[0038] Advantageously, the first face of the first substrate is made of a dielectric material, preferably SiO2 or SisN / i, a semiconductor material or a metal nitride such as TiN, WN, AIN (the wettability layer will then preferably be made of metal) and / or the first face of the second substrate is made of a dielectric material, preferably SiO2 or SisN / i, or a semiconductor material or a metal nitride such as TiN, WN, AIN (the wetting layer will then preferably be made of metal).

[0039] Advantageously, the eutectic alloy is chosen from Al-Ge, Au-ln, Au-Sn, Au-Si, Bi-Sn and Au-Ge.

[0040] Advantageously, the first material is chosen from AISi or AlCu for the eutectic alloy AIGe, Au for the eutectic alloy Au-ln, Au-Sn, Au-Si or Au-Ge, Bi for the eutectic alloy Bi-Sn and / or the second material is chosen from Ge for the eutectic alloy Al-Ge or Au-Ge, Sn for the eutectic alloy Au-Sn or Bi-Sn, Si for the eutectic alloy Au-Si, In for the eutectic alloy Au-ln.

[0041] The first element has a volume VI and the second element has a volume V2. The volumes VI and V2 are chosen so as to form a eutectic alloy with the relative concentrations given by VI and V2. The volumes and relative compositions of the two elements are chosen so as to correspond to the eutectic concentration.

[0042] According to a first advantageous embodiment, the first bead is arranged on the first wettability layer, the wettability layer protruding either on one side of the first bead or on either side of the first bead and / or the second bead is arranged on the second wettability layer, the wettability layer protruding either on one side of the second bead or on either side of the second bead.

[0043] According to a second advantageous embodiment, the wettability layer(s) is / are offset relative to the first bead and / or relative to the second bead, the wettability layer(s) being connected to the first bead and / or to the second bead by crosspieces if necessary. The crosspieces are advantageously made of the same material as the wettability layer.

[0044] The invention also relates to a device thus obtained. The device comprises a first substrate and a second substrate sealed to each other by a sealing bead based on a eutectic alloy, at least one of the first substrate and the second substrate being locally covered by a wettability layer, the contact angle of a drop of eutectic alloy on the wettability layer being lower, on the one hand, than the contact angle of eutectic alloy on the first face of the first substrate and, on the other hand, than the contact angle of eutectic alloy on the first face of the second substrate, drips of the eutectic alloy being trapped on the wettability layer.

[0045] Advantageously, the wettability layer is a metallic layer, preferably chosen from W, Ti, Al, Au and Cu, the first face of the first substrate is made of a dielectric material, preferably SiO2, or a semiconductor material and / or the first face of the second substrate is made of a dielectric material, preferably SiO2, or a semiconductor material.

[0046] Advantageously, the eutectic alloy is chosen from Al-Ge, Au-ln, Au-Sn, Au-Si, Bi-Sn and Au-Ge.

[0047] According to a first advantageous embodiment, the sealing bead is arranged on the wettability layer, the wettability layer protruding either on one side of the sealing bead or on either side of the sealing bead.

[0048] According to a second advantageous embodiment, the wettability layer is offset locally relative to the sealing bead, the wettability layer being connected to the sealing bead by crosspieces. The crosspieces are, advantageously, made of the same material as the wettability layer.

[0049] Other characteristics and advantages of the invention will emerge from the additional description which follows.

[0050] It goes without saying that this additional description is given only as an illustration of the subject of the invention and must in no case be interpreted as a limitation of this subject.

[0051] BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The present invention will be better understood by reading the description of exemplary embodiments given purely for informational purposes and in no way limiting, with reference to the appended drawings in which:

[0053] Figures 1A and 1B, previously described, schematically represent different stages of a eutectic sealing method according to the prior art. Figure 2, previously described, is a photograph showing drips of a eutectic alloy resulting from a method of the prior art, as shown in Figures 1A and 1B.

[0054] Figures 3A and 3B schematically represent different stages of a eutectic sealing method according to a particular embodiment of the invention.

[0055] Figures 4A and 4B schematically represent different stages of a eutectic sealing method according to another particular embodiment of the invention.

[0056] Figures 5A and 5B schematically represent different stages of a eutectic sealing method according to another particular embodiment of the invention.

[0057] Figures 6A and 6B schematically represent different stages of a eutectic sealing method according to another particular embodiment of the invention.

[0058] Figure 7 shows, schematically and in top view, a cord arranged on a wettability layer, according to a particular embodiment of the invention.

[0059] Figures 8A and 8B schematically represent different stages of a eutectic sealing method according to another particular embodiment of the invention; the wettability layer and the bead shown in section in Figure 8A correspond to those of Figure 9, according to the section defined by the dashed line.

[0060] Figure 9 shows, schematically and in top view, a bead of material placed on a wettability layer, according to a particular embodiment of the invention.

[0061] The different parts represented in the figures are not necessarily on a uniform scale, to make the figures more readable.

[0062] The various possibilities (variants and embodiments) are to be understood as not being mutually exclusive and may be combined with each other. Furthermore, in the following description, terms that depend on the orientation, such as "above", "below", etc. of a structure apply considering that the structure is oriented in the manner illustrated in the figures.

[0063] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0064] We will now describe in more detail the method of eutectic sealing of two substrates with reference to the attached figures 3A and 3B, 4A and 4B, 5A and 5B, 6A and 6B, 7, 8A and 8B, 9.

[0065] The method for eutectic sealing of two substrates comprises the following steps: a) providing a first substrate 111 having a first face covered by a first bead 121 made of a first material, and optionally by one or more microelectronic devices 140, the first material comprising a first element, b) providing a second substrate 112 having a first face covered by a second bead 122 made of a second material, and optionally by one or more microelectronic devices 140, the second material comprising a second element, capable of forming a eutectic alloy with the first element, c) bringing the first bead 121 and the second bead 122 into contact, d) carrying out a heat treatment to form a eutectic phase combining the first element provided by the first bead and the second element provided by the second bead,whereby a sealing bead 123 based on the eutectic alloy is formed and the first substrate 111 is sealed to the second substrate 112 with the sealing bead 123.,

[0066] The sealing bead 123 obtained and the two substrates 121, 122 delimit a hermetic cavity in which one or more microelectronic devices 140 are advantageously arranged. The encapsulation pressure prevailing in the cavity is variable depending on the application envisaged and is, typically, between 10 -3 mbar and 1 bar (i.e. between 0.1 Pa and 100,000 Pa).

[0067] In this method, at least one of the first substrate 111 provided in step a) and the second substrate 112 provided in step b) is locally covered by a wettability layer 130, whereby in step c), the drips 123' of the eutectic alloy form on the wettability layer 130 and are contained at least partially, and preferably, totally at this layer 130.

[0068] Each substrate 111, 112 provided in step a) and in step b) comprises two main faces parallel to each other. The first face of the first substrate 111 is intended to be placed opposite the first face of the second substrate 112.

[0069] The substrates 111 and 112 may be made mainly of the same material or the substrates 111 and 112 may be made of different materials. These materials may be chosen from Si, Ge, InP, AsGa, AI2O3, SiC, GaN, LNO, LTO.

[0070] The first substrate 111 and / or the second substrate 112 may comprise a support substrate covered by a thin layer. The thin layer then forms the first face of the first substrate or the first face of the second substrate.

[0071] The first face of the first substrate 111 and / or the first face of the second substrate 112 may be made of a dielectric material SiO2, SisIX or a metal nitride such as TiN, WN or AIN.

[0072] Preferably, the first face of the first substrate 111 and / or the first face of the second substrate 112 are made of oxide, for example SiO2. It may be a native oxide layer, a thermal oxide layer or a deposited oxide layer.

[0073] Thus, it is possible to have a first substrate 111 comprising a Si support substrate covered by a thin layer of SiO2. The same applies to the second substrate 112.

[0074] The first face of the first substrate 111 and / or the first face of the second substrate 112 may be of identical nature or of different natures.

[0075] The first substrate and the second substrate each have, for example, a thickness of between 300 pm and 1000 pm.

[0076] One or more microelectronic devices 140 may be arranged on the first face of the first substrate 111 and / or on the first face of the second substrate 112. The microelectronic devices of the first substrate 111 may be identical to or different from those present on the second substrate 112. By microelectronic device is meant a microelectronic component, such as, for example, a microsystem of the MEMS (“Micro-Electro-Mechanical Systems”), NEMS (“Nano-Electro-Mechanical Systems”), MOEMS (“Micro-Opto-Electro-Mechanical Systems”), or NOEMS (“Nano-Opto-Electro-Mechanical Systems”) type. For example, it may be an infrared micro-detector, transistor, microbattery, capacitor, super-capacitor, photovoltaic component, accelerometer, pressure sensor, microphone, antenna, gyrometer or gyroscope, or any other device deemed necessary for the production of the final object.

[0077] The first material of the first cord 121 may be chosen from AISi or AlCu for the eutectic alloy AIGe, Au for the eutectic alloy Au-ln, Au-Sn, Au-Si or Au-Ge, Bi for the eutectic alloy Bi-Sn.

[0078] The second material of the second cord 122 may be chosen from Ge for the eutectic alloy Al-Ge or Au-Ge, Sn for the eutectic alloy Au-Sn or Bi-Sn, Si for the eutectic alloy Au-Si, In for the eutectic alloy Au-In.

[0079] Preferably, the first material comprises aluminum and the second material comprises germanium to form the eutectic alloy AIGe.

[0080] The first material may be made of the first element and / or the second material may be made of the second element.

[0081] For example, the first material might be aluminum and the second material might be germanium.

[0082] It is also possible as described previously to have symmetrical or asymmetrical configurations.

[0083] It is possible, for example, to have a first cord in the form of a multilayer comprising a layer of aluminum covered by a thin layer of germanium (for example the thin layer has a thickness of 10 nm) and a second cord made of germanium.

[0084] It is possible to deposit an additional layer on the first face of the first substrate and the first material and / or on the first face of the second substrate and the second material. For example, it is possible to deposit a thin layer of Ge on aluminum itself deposited on a layer of SiO2. The wetting layer can be deposited later. For example, it is possible to deposit a 10 nm layer of Ge on the aluminum. The presence of the Ge layer favors the reaction between aluminum and Germanium by facilitating the start of the reaction on the aluminum despite the presence of an aluminum oxide layer that can form. When the entire surface of the substrate is covered by this Ge layer, the devices are formed on this layer. It is also possible to remove part of the Ge layer and possibly part of the aluminum layer if necessary.

[0085] This layer is generally applied just before the bonding step.

[0086] Preferably, the wettability layer 130 is a metal layer. Advantageously, the wettability layer is made of W, Ti, Al, Au or Cu.

[0087] According to a very advantageous embodiment, the wettability layer 130 is a metal layer, the first face of the first substrate 111 is made of a dielectric, semiconductor or metal nitride material and the first face of the second substrate 112 is made of a dielectric, semiconductor or metal nitride material.

[0088] The wettability of the eutectic is better on the wettability layer 130 than on the first face of the first substrate 111 or on the first face of the second substrate 112. Thus, the eutectic alloy will remain on the wettability layer 130 rather than flowing onto the substrates.

[0089] By "the wettability of the eutectic is better" is meant that the contact angle of the eutectic drop on the first face of the first substrate 111 or on the first face of the second substrate 112 is at least 20° and preferably at least 40° greater than the contact angle of the eutectic drop on the wettability layer 130.

[0090] For example, the contact angle of the AIGe drop on a SiO2 face is greater than 110° (thesis V. Lumineau). The silicon oxide is therefore not wetted by the Al-Ge eutectic alloy. Thus, a wettability layer 130 for which the contact angle of the AIGe drop on this layer is less than or equal to 90°, preferably less than or equal to 70° will be advantageously chosen.

[0091] In order to determine the contact angle of the eutectic alloy drop, the method used is, for example, that described in V. Lumineau's thesis. The contact angle measurement is that of the placed drop: we observe the shape of a drop of the eutectic alloy formed on a flat face for a temperature higher than its melting temperature. For this, the alloy is placed in an alumina crucible which ends with a capillary of diameter 0.6 mm. Once the melting has taken place and the experimental temperature reached, a piston allows to form a drop at the end of the capillary. The crucible is then lowered towards the solid face to be studied and the drop is deposited. The observations are carried out in situ, at temperature, using a camera (25 images / s) and through a window. The video recording of the spreading of the drop then allows the measurement and calculation of the intrinsic parameters of the drops via the Drop Shape Analysis software.A pumping system allows a high vacuum of up to 5.10' to be obtained. 7 mbar (or 5.10' 5 Pa).

[0092] The wettability layer 130 can be arranged in several configurations.

[0093] The wettability layer 130 may be disposed between the first substrate 111 and the first bead 121 (FIGS. 4A and 4B), and / or between the second substrate 112 and the second bead 122 (FIGS. 3A and 3B).

[0094] The wettability layer 130 protrudes from the bead 121, 122 so as to have a free face to contain the drip 123'. The wettability layer 130 may protrude on either side of the bead 121, 122. Alternatively, it may protrude only on one side of the bead 121, 122. The overhang zone of the wettability layer 130 may be between a few tens of nanometers and a few hundreds of micrometers.

[0095] The wettability layer 130 may protrude on either side of the bead 121, 122 which covers it (figures 3A and 3B, 4A and 4B).

[0096] Alternatively, the wettability layer may protrude only on one side of the bead (Figures 5A and 5B, 6A and 6B, 7). Advantageously, the wettability layer 130 protrudes only outside the cavity formed by the sealing bead 123 and the two substrates to guide the eutectic drips 123' outside the cavity containing the chip microelectronic device(s) and preserve them.

[0097] According to another embodiment variant, the wettability layer 130 may be arranged next to the bead 121, 122 (FIGS. 8A and 8B, 9). It may be in contact with the bead 121, 122 or be offset relative to the bead 121, 122 (i.e. the wettability layer does not touch the bead). For example, the wettability layer 130 forms a belt around the bead. Crosspieces (or 'bridges') may facilitate the evacuation of drips towards the wettability layer. The crosspieces may be made of a material identical to or different from that of the wettability layer. Preferably, the wettability layer 130 is located only outside the sealing bead (i.e. outside the cavity) and is separate from the sealing bead.

[0098] A single wettability layer 130 has been described. It is also possible to have a wettability layer on each substrate 111, 112.

[0099] Alternatively, the first substrate 111 and the second substrate 112 are each locally covered by a wettability layer 130, whereby during step c), the drips 123' of the eutectic alloy form on the wettability layers 130 and are contained at least partially, and preferably, totally at the level of these layers.

[0100] The use of two wettability layers allows for better confinement of the eutectic material and thus stabilization. Such a configuration can also allow for the reduction of the dimensions of these layers compared to a single wettability layer, which is particularly advantageous for miniaturizing devices.

[0101] The two layers can be arranged on each substrate in the same way or in a different way.

[0102] The size of the wettability layer 130 will be determined based on the size of the beads. Its size will be chosen so as to contain the drips.

[0103] During step c), the two beads 121, 122, or even the two substrates 111, 112, are brought into intimate contact with each other and then the heat treatment is carried out. The treatment can be carried out under a controlled atmosphere (vacuum, inert atmosphere) and / or with mechanical pressure to contact the entire face. For example, a force greater than or equal to 2 kN or 10 kN or even 30 kN can be applied.

[0104] The temperature is chosen according to the eutectic alloy. The temperature is chosen so as to reach, or even exceed, the melting temperature of the eutectic alloy, to form a solder based on the eutectic alloy between the substrates 111, 112 to be assembled. Preferably, the temperature applied is lower than the melting temperature of the first bead 121, and the melting temperature of the second bead 122. For example, to produce the eutectic alloy Al-Ge, a temperature higher than 425°C (melting temperature of the eutectic alloy) will be applied.

[0105] The sealing bead 123 is made of a eutectic alloy comprising two elements, one coming from the first element of the first bead and the other coming from the second element of the second bead. This alloy is also called brazing.

[0106] The formation of the 123 eutectic alloy cord ensures the strong mechanical strength of the seal.

[0107] The sealing bead 123 has, for example, a width of between 30 μm and 200 μm. The width will be chosen so as to be sufficiently high to allow good sealing while being low enough to allow miniaturization.

[0108] The sum of the thicknesses of the first and second materials is generally between 100 nm and 10 pm. Preferably it will be 1 pm.

[0109] The use of a wetting layer may be combined with the use of a mechanical stop as described in the prior art.

[0110] The process described above allows the production of assemblies with a thickness of less than 10 μm. In addition, the seal has few hole-type defects at the interfaces compared to thermo-compression, which is interesting for assemblies requiring a controlled atmosphere.

Claims

CLAIMS 1. A method for eutectic sealing of two substrates (111, 112) comprising the following steps: a) providing a first substrate (111) having a first face covered by a first bead (121) made of a first material, and optionally by one or more microelectronic devices (140), the first material comprising a first element, b) providing a second substrate (112) having a first face covered by a second bead (122) made of a second material, and optionally by one or more microelectronic devices (140), the second material comprising a second element, capable of forming a eutectic alloy with the first element, c) bringing the first bead (121) and the second bead (122) into contact, and carrying out a heat treatment to form a eutectic phase alloying the first element of the first bead (121) and the second element of the second bead (122),whereby a sealing bead (123) based on the eutectic alloy is formed and the first substrate (111) is sealed to the second substrate (112), the formation of the eutectic phase being accompanied by the formation of drips (123') of eutectic alloy, a method characterized in that at least one of the first substrate (111) and the second substrate (112) is locally covered by a wettability layer (130), the contact angle of a drop of eutectic alloy on the wettability layer (130) being at least 20° and preferably at least 40° lower, on the one hand, than the eutectic alloy contact angle on the first face of the first substrate (111) and, on the other hand, than the eutectic alloy contact angle on the first face of the second substrate (112), whereby during step c), the drips (123') of eutectic alloy form on the wettability layer (130)., 2. Method according to claim 1, characterized in that the first cord (121) comprises the first material and the second material, the first cord (121) being for example in the form of a multilayer, and / or in that the second cord (122) comprises the first material and the second material, the second bead (122) being for example in the form of a multilayer.

3. Method according to one of claims 1 to 2, characterized in that the wettability layer (130) is a metal layer, preferably chosen from W, Ti, Al, Au and Cu, or a metal nitride layer, for example a layer of TiN, AIN or WN.

4. Method according to any one of the preceding claims, characterized in that the first face of the first substrate (111) is made of a dielectric material, preferably SiO2 or SisN / i, a semiconductor material or metal nitride and / or in that the first face of the second substrate (112) is made of a dielectric material, preferably SiO2 or SisN / i, a semiconductor material or metal nitride.

5. Method according to any one of the preceding claims, characterized in that the eutectic alloy is chosen from Al-Ge, Au-ln, Au-Sn, Au-Si, Bi-Sn and Au-Ge.

6. Method according to the preceding claim, characterized in that the first material is chosen from AISi or AlCu for the eutectic alloy AIGe, Au for the eutectic alloy Au-ln, Au-Sn or Au-Si and / or in that the second material is chosen from Ge for the eutectic alloy Al-Ge, Sn for the eutectic alloy Au-Sn or Bi-Sn, Si for the eutectic alloy Au-Si.

7. Method according to any one of claims 1 to 6, characterized in that the first bead (121) is arranged on the wettability layer (130), the wettability layer (130) protruding either on one side of the first bead (121) or on either side of the first bead (121) or in that the second bead (122) is arranged on the wettability layer (130), the wettability layer (130) protruding either on one side of the second bead (122) or on either side of the second bead (122).

8. Method according to any one of claims 1 to 6, characterized in that the wettability layer (130) is offset relative to the first bead (121) or relative to the second bead (122), the wettability layer (130) being connected to the first bead (121) or to the second bead (122) by crosspieces.

9. Device comprising a first substrate (111) and a second substrate (112) sealed to each other by a sealing bead (123) based on a eutectic alloy, at least one of the first substrate (111) and the second substrate (112) being locally covered by a wettability layer (130), the contact angle of a drop of eutectic alloy on the wettability layer (130) being lower, on the one hand, than the contact angle of eutectic alloy on the first face of the first substrate (111) and, on the other hand, than the contact angle of eutectic alloy on the first face of the second substrate (112), drips (123') of the eutectic alloy being arranged on the wettability layer (130).

10. Device according to claim 9, characterized in that the wettability layer (130) is a metal layer, preferably chosen from W, Ti, Al, Au and Cu, or a metal nitride layer, for example a TiN, AIN or WN layer, and in that the first face of the first substrate (111) is made of a dielectric material, preferably SiO2 or SisN / i, a semiconductor material or a metal nitride and / or in that the first face of the second substrate (112) is made of a dielectric material, preferably SiO2 or SisN / i, or a semiconductor material or a metal nitride.

11. Device according to one of claims 9 to 10, characterized in that the eutectic alloy is chosen from Al-Ge, Au-ln, Au-Sn, Au-Si, Bi-Sn and Au-Ge.

12. Device according to one of claims 9 to 11, characterized in that the sealing bead (123) is arranged on the wettability layer (130), the layer of wettability (130) protruding either on one side of the sealing bead (123) or on either side of the sealing bead (123).

13. Device according to one of claims 9 to 11, characterized in that the wettability layer (130) is offset locally relative to the sealing bead (123), the wettability layer (130) being connected to the sealing bead (123) by crosspieces.

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