Method for eutectic sealing of two substrates

Abstract

A method comprising the steps of: a) providing a first substrate (111) covered by a first bead (121), the first bead (121) comprising a first element, b) providing a second substrate (112) covered by a second bead (122), the second bead (122) comprising a second element, c) contacting the first bead (121) and the second bead (122) and heat treating to form a eutectic phase bonding the first element and the second element, the first substrate (111) is sealed to the second substrate (112), whereby a bond 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 a cast portion (123 '), at least one of the first substrate (111) and / or the second substrate (112) being partially covered by a wetting layer (130), whereby during step c) the cast portion (123') of the eutectic alloy is formed on the wetting layer (130).

Description

Technical Field

[0001] The present invention relates to the field of microelectronics, and more particularly to the packaging (or encapsulation) of microelectronic devices, such as microsystems of the MEMS ("Micro-Electro-Mechanical System"), NEMS ("Nano-Electro-Mechanical System"), MOEMS ("Micro-Opto-Electro-Mechanical System") or NOEMS ("Nano-Opto-Electro-Mechanical System") type, including encapsulating or enclosing the device in a sealed cavity and controlling the atmosphere in the cavity.

[0002] The present invention relates to a method for hermetically sealing two substrates.

[0003] The present invention also relates to a device obtained by this method.

[0004] The present invention can be applied to many industrial fields, such as the fields of motor vehicles, mobile phones or video game consoles.

[0005] The present invention is particularly interesting because it allows the substrates to be hermetically sealed with a eutectic alloy while avoiding the risk of short-circuiting of moving structures or mechanical jamming. Background Art

[0006] Microelectronic devices of the MEMS, NEMS, MOEMS or NOEMS type are sensors or actuators of nanometer or micrometer size. They are manufactured by microelectronic methods.

[0007] Encapsulating these microelectronic devices can, on the one hand, protect them from external factors (such as moisture, particulate contamination, active elements such as oxygen, etc.), and on the other hand, control the atmosphere (such as pressure, encapsulation gas composition, etc.) in the device encapsulation cavity. The encapsulation pressure in the cavity can be adjusted according to the intended use, usually between 10 -3 mbar and 1 bar.

[0008] This encapsulation can use various types of seals: thermocompression, eutectic sealing, anodic sealing, etc.

[0009] Currently, eutectic sealing seems to be the most promising.

[0010] Generally, as shown in FIGS. 1A and 1B, in the eutectic sealing method, alloy components are respectively deposited on the surfaces of the substrates 11, 12 to be assembled. A first solder ball 21 with the material is formed on the first substrate 11. A second solder ball 22 with the material is formed on the second substrate 12 (FIG. 1A).

[0011] During the sealing process, two substrates 11, 12 are brought into close contact, and a certain temperature is applied to the entire system. If the relative compositions of the two materials match the eutectic concentration, melting occurs at the eutectic temperature. In the liquid phase, a homogeneous liquid composed of the two materials exists between the two surfaces. Then, the solidification of the solder will result in the formation of a material that is composed of the materials used to achieve eutectic melting undergoing phase separation within their respective solubility ranges. Even if this material is not composed of a single phase, it is still called a eutectic material. This eutectic material is located between the two substrates 11, 12 and allows for mechanical closure of the interface, thereby forming the final assembly.

[0012] Therefore, the eutectic material undergoes a liquid state, then solidifies and forms a sealing bead 23 (Figure 1B) around the chip to be encapsulated.

[0013] However, liquid-phase channels may accompany the outflow of the eutectic material from the sealing bead region (Figure 2). These run-outs 23' may, after solidification, cause mechanical blockage of the moving structure and / or create short circuits between various regions of the device.

[0014] Therefore, it is necessary to control the leakage of the liquid solder.

[0015] For example, in the paper "Study of the bonding of MEMS by Al-Ge eutectic alloy" by V. Lumineau in 2018, he proposed to set stop devices near the bead. These stop devices limit the approach between the two plates to be assembled, thereby preventing the extrusion of the Al-Ge bilayer film. However, in order for this solution to be effective, solid stop devices need to be set at a certain distance on both sides of the bead. However, due to various limitations in structural compactness, this solution is not applicable to all devices. Summary of the Invention

[0016] An object of the present invention is to propose a eutectic sealing method that overcomes the drawbacks of the prior art and allows for airtight sealing of two substrates while avoiding short circuits and mechanical blockage phenomena.

[0017] To this end, the present invention proposes a method for eutectic sealing of two substrates, comprising the following steps:

[0018] a) Providing a first substrate having a first surface covered with a first bead made of a first material and optionally covered with one or more microelectronic devices, the first material comprising a first element,

[0019] b) Provide a second substrate having a first face covered with second solder balls made of a second material and optionally covered with one or more microelectronic devices, the second material including a second element capable of forming a eutectic alloy with the first element,

[0020] c) Place the first solder ball and the second solder ball in contact and perform a heat treatment to form a eutectic phase that alloys the first element of the first solder ball with the second element of the second solder ball, thereby forming a hermetic solder ball containing a eutectic alloy, and the first substrate is sealed to the second substrate, and the formation of the eutectic phase is accompanied by the formation of a cast portion of the eutectic alloy.

[0021] It is also possible to use a first solder ball including a first material and a second material, for example in the form of a multilayer, and / or a second solder ball including a first material and a second material, for example in the form of a multilayer.

[0022] Thus, a symmetric configuration can be formed.

[0023] Similarly, an asymmetric structure can also be formed. For example, by providing a first solder ball containing a first material and a second solder ball containing a second material, a portion of the first material has been deposited on the second material. In this case, the first material on the first face of the first substrate is thinner to maintain the eutectic concentration before melting.

[0024] According to another alternative embodiment, the asymmetric structure is achieved by providing a second solder ball containing a second material and a first solder ball containing a first material, and a portion of the second material has been deposited on the first solder ball. In this case, the second material on the first face of the second substrate is thinner to maintain the eutectic concentration before melting.

[0025] It is possible to modify the material distribution on only one of the two faces or modify the material distribution on both faces.

[0026] Advantageously, a configuration that results in the formation of an atomic flow through the bonding interface is adopted, that is, an asymmetric configuration is adopted.

[0027] In this method, at least one of the first substrate and the second substrate is locally covered with a wetting layer, and the contact angle of the eutectic alloy droplet on the wetting layer is at least 20°, preferably at least 40°, smaller than the contact angle of the eutectic alloy on the first face of the first substrate on the one hand, and the contact angle of the eutectic alloy droplet on the wetting layer is at least 20°, preferably at least 40°, smaller than the contact angle of the eutectic alloy on the first face of the second substrate on the other hand. Thus, during step c), the cast portion of the eutectic alloy preferably enters the wetting layer.

[0028] The fundamental difference between the present invention and the prior art lies in that at least one region of preferential wettability is provided in the eutectic alloy opposite to the substrate. The wettability of the eutectic material formed during step c) on the wetting layer is better than that on the surfaces of the first substrate and the second substrate.

[0029] Therefore, instead of setting a "physical" barrier (such as a stop device in the prior art), we adopt a so-called "energy" barrier, the surface of which has a relatively high surface energy for liquid metal, while the wetting region has a relatively low surface energy. The liquid metal wets this wetting region just like falling into a potential well. By cleverly integrating the preferential wetting layer, the outflow of the eutectic material is guided and kept within a region "risk-free" for the chip function.

[0030] For example, for the eutectic alloy Al-Ge, this alloy has better wettability on the metal surface than on the dielectric material surface. A metal wetting layer is provided near the position of the sealing bead or at the position in contact with the sealing bead, allowing the inclusion of a casting part when the substrate surface is made of a dielectric material.

[0031] In particular, a substrate with a contact angle of the liquid droplet of the eutectic alloy greater than or equal to 90°, preferably greater than or equal to 100°, is selected.

[0032] For example, a wetting layer with a contact angle of the liquid droplet of the eutectic alloy less than or equal to 70°, preferably less than or equal to 60°, and even more preferably less than or equal to 40°, is selected.

[0033] By adopting this sealing method, the molten metal alloy adheres to the surface of the substrate to be assembled, and the casting part is included within the wetting layer. The cavity sealed in this way has good airtightness, and the component has good mechanical strength.

[0034] Advantageously, the wetting layer (also called the infiltration layer) is a metal layer. Preferably, the metal layer is made of a metal selected from W, Ti, Al, Au, and Cu.

[0035] According to another advantageous alternative, the wetting layer is a metal nitride layer, such as TiN, WN, AlN.

[0036] According to another advantageous alternative, the wetting layer is a semiconductor layer, such as Si, Ge, SiC, AsGa, InP layer.

[0037] Advantageously, the first face of the first substrate is made of a dielectric material (preferably SiO2 or Si3N4), a semiconductor material or a metal nitride (such as TiN, WN, AlN) (the wetting layer is preferably made of a metal), and / or the first face of the second substrate is made of a dielectric material (preferably SiO2 or Si3N4) or a semiconductor material or a metal nitride (such as TiN, WN, AlN) (the wetting layer is preferably made of a metal).

[0038] Advantageously, the eutectic alloy is selected from Al-Ge, Au-In, Au-Sn, Au-Si, Bi-Sn and Au-Ge.

[0039] Advantageously, for the eutectic alloy AlGe, the first material is selected from AlSi or AlCu, for the eutectic alloys Au-In, Au-Sn, Au-Si or Au-Ge, the first material is selected from Au, for the eutectic alloy Bi-Sn, the first material is selected from Bi, and / or for the eutectic alloy Al-Ge, the second material is selected from Ge, for the eutectic alloys Au-Sn or Bi-Sn, the second material is selected from Sn, for the eutectic alloy Au-Si, the second material is selected from Si, for the eutectic alloy Au-In, the second material is selected from In.

[0040] The volume of the first element is V1 and the volume of the second element is V2. The volumes V1 and V2 are chosen so as to form a eutectic alloy given by the relative concentrations of V1 and V2. The relative volumes and compositions of the two elements should correspond to the eutectic concentration.

[0041] According to a first advantageous embodiment, a first solder ball is provided on a first wetting layer, the wetting layer protruding on either side or on both sides of the first solder ball, and / or a second solder ball is provided on a second wetting layer, the wetting layer protruding on either side or on both sides of the second solder ball.

[0042] According to a second preferred embodiment, the wetting layer is offset relative to the first solder ball and / or the second solder ball, and the wetting layer is optionally connected to the first solder ball and / or the second solder ball by a lateral member. The lateral member is preferably made of the same material as the wetting layer.

[0043] The invention also relates to a device thus obtained. The device comprises a first substrate and a second substrate, the first substrate and the second substrate being sealed to each other by a sealing solder ball comprising a eutectic alloy, at least one of the first substrate and the second substrate being locally covered by a wetting layer, the contact angle of a droplet of the eutectic alloy on the wetting layer being less than, on the one hand, the contact angle of the eutectic alloy on the first face of the first substrate and less than, on the other hand, the contact angle of the eutectic alloy on the first face of the second substrate, and the cast portion of the eutectic alloy being trapped on the wetting layer.

[0044] Advantageously, the wetting layer is a metal layer, preferably selected from W, Ti, Al, Au, and Cu, and 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.

[0045] Advantageously, the eutectic alloy is selected from Al-Ge, Au-In, Au-Sn, Au-Si, Bi-Sn, and Au-Ge.

[0046] According to a first advantageous embodiment, the sealing bead is disposed on the wetting layer, and the wetting layer protrudes from either side or both sides of the sealing bead.

[0047] According to a second preferred embodiment, the wetting layer is locally offset relative to the sealing bead and is connected to the sealing bead by a lateral member. Advantageously, the lateral member is made of the same material as the wetting layer.

[0048] Other features and advantages of the present invention will become apparent from the following additional description.

[0049] It is understood that this additional description is only an exemplary description of the purpose of the present invention and should in no way be construed as a limitation of that purpose. Description of the Drawings

[0050] The present invention will be better understood by reading the description of the exemplary embodiments given for reference only and not in any way limiting the purpose, in conjunction with the drawings, in which:

[0051] The foregoing FIGS. 1A and 1B schematically illustrate the respective steps of a eutectic sealing method according to the prior art.

[0052] The foregoing FIG. 2 is an image showing a cast portion of a eutectic alloy produced by the prior art method as shown in FIGS. 1A and 1B.

[0053] Figure 3A and Figure 3B schematically illustrate the respective steps of a eutectic sealing method according to a specific embodiment of the present invention.

[0054] Figure 4A and Figure 4B schematically illustrate the respective steps of a eutectic sealing method according to another specific embodiment of the present invention.

[0055] Figure 5A and Figure 5B schematically illustrate the respective steps of a eutectic sealing method according to another specific embodiment of the present invention.

[0056] Figure 6A and Figure 6BSchematically shows the steps of a eutectic sealing method according to another specific embodiment of the present invention.

[0057] Figure 7 Schematically shows in a top view a solder ball disposed on a wetting layer according to a specific embodiment of the present invention.

[0058] Figure 8A and Figure 8B Schematically shows the steps of a eutectic sealing method according to another specific embodiment of the present invention; according to the cross-section defined by the dashed line, Figure 8A the wetting layer and the solder ball shown in the cross-section in Figure 9 correspond to the wetting layer and the solder ball in

[0059] Figure 9 Schematically shows in a top view a solder ball of a material disposed on a wetting layer according to a specific embodiment of the present invention.

[0060] For clarity of the drawings, the various parts shown in the drawings do not necessarily have a uniform scale.

[0061] All possibilities (alternatives and embodiments) should be understood as not being mutually exclusive and can be combined together.

[0062] In addition, in the following description, terms depending on the orientation of the structure (such as "top", "bottom", etc.) apply, while considering the structure to be oriented as shown in the figures. Detailed Description

[0063] Now reference will be made to the appended Figure 3A and Figure 3B 、 Figure 4A and Figure 4B 、 Figure 5A and Figure 5B 、 Figure 6A and Figure 6B 、 Figure 7 、 Figure 8A and Figure 8B 、 Figure 9 describe in more detail a method for eutectic sealing of two substrates.

[0064] The method for eutectic sealing of two substrates includes the following steps:

[0065] a) Providing a first substrate 111 having a first surface covered with a first solder ball 121 made of a first material and optionally covered with one or more microelectronic devices 140, the first material including a first element,

[0066] b) Provide a second substrate 112 having a first surface covered by second solder balls 122 made of a second material and optionally covered by one or more microelectronic devices 140, the second material including a second element capable of forming a eutectic alloy with the first element,

[0067] c) Place the first solder ball 121 and the second solder ball 122 in contact with each other,

[0068] d) Perform a heat treatment to form a eutectic phase in which the first element provided by the first solder ball and the second element provided by the second solder ball are alloyed, thereby forming a hermetic solder ball 123 containing a eutectic alloy, and seal the first substrate 111 to the second substrate 112 through the hermetic solder ball 123.

[0069] The obtained hermetic solder ball 123 and the two substrates 121, 122 together define a hermetic cavity, in which one or more microelectronic devices 140 are preferably provided. The packaging pressure in the cavity can be adjusted according to the intended use, usually between 10 -3 mbar and 1 bar (or between 0.1 Pa and 100,000 Pa).

[0070] 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 wetting layer 130, so that during step c), a cast portion 123' of the eutectic alloy is formed on the wetting layer 130 and is at least partially, preferably completely, contained in the layer 130.

[0071] Each of the substrates 111 and 112 provided in steps a) and b) includes two main surfaces parallel to each other. The first surface of the first substrate 111 is placed facing the first surface of the second substrate 112.

[0072] The substrates 111, 112 may be mainly made of the same material, or the substrates 111 and 112 may be made of different materials. These materials may be selected from Si, Ge, InP, AsGa, Al2O3, SiC, GaN, LNO, LTO.

[0073] The first substrate 111 and / or the second substrate 112 may include a support substrate covered with a thin layer. The thin layer thus forms the first surface of the first substrate or the first surface of the second substrate.

[0074] The first surface of the first substrate 111 and / or the first surface of the second substrate 112 may be made of a dielectric material such as SiO2, Si3N4 or a metal nitride such as TiN, WN or AlN.

[0075] Preferably, the first surface of the first substrate 111 and / or the first surface of the second substrate 112 are made of an oxide, such as SiO2. The oxide can be a natural oxide layer, a thermal oxide layer, or an oxide deposition layer.

[0076] Thus, the first substrate 111 can comprise a support substrate made of Si, which is covered by a thin layer of SiO2. The same applies to the second substrate 112.

[0077] The first surface of the first substrate 111 and / or the first surface of the second substrate 112 can have the same properties or different properties.

[0078] The thickness of each of the first substrate and the second substrate is, for example, between 300 μm and 1,000 μm.

[0079] One or more microelectronic devices 140 can be provided on the first surface of the first substrate 111 and / or on the first surface of the second substrate 112. The microelectronic devices on the first substrate 111 can be the same as or different from the microelectronic devices on the second substrate 112.

[0080] Microelectronic devices mean microelectronic components, such as microsystems 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 can be an infrared microdetector, a transistor, a microbattery, a capacitor, a supercapacitor, a photovoltaic module, an accelerometer, a pressure sensor, a microphone, an antenna, a rate gyroscope or a gyroscope, and any other device considered necessary to achieve the final goal.

[0081] The first material of the first solder ball 121 can be selected from: AlSi or AlCu for the eutectic alloy AlGe, Au for the eutectic alloys Au-In, Au-Sn, Au-Si or Au-Ge, and Bi for the eutectic alloy Bi-Sn.

[0082] The second material of the second solder ball 122 can be selected from: Ge for the eutectic alloys Al-Ge or Au-Ge, Sn for the eutectic alloys Au-Sn or Bi-Sn, Si for the eutectic alloy Au-Si, and In for the eutectic alloy Au-In.

[0083] Preferably, the first material comprises aluminum and the second material comprises germanium to form the eutectic alloy AlGe.

[0084] The first material can consist of a first element and / or the second material can consist of a second element.

[0085] For example, the first material can be aluminum and the second material can be germanium.

[0086] As described above, it may also have a symmetric or asymmetric configuration.

[0087] For example, it may have a first solder ball in the form of multiple layers, including an aluminum layer, a thin layer of germanium covering it (e.g., the thickness of this thin layer is 10 nm), and a second solder ball composed of germanium.

[0088] An additional layer may be deposited on the first side of the first substrate and the first material and / or on the first side of the second substrate and the second material. For example, a thin layer of Ge may be deposited on aluminum deposited on a SiO2 layer. The wetting layer may then be removed. For example, a 10-nm Ge layer may be deposited on aluminum. Although an aluminum oxide layer may be formed, the presence of the Ge layer can promote the reaction start on aluminum, thus promoting the reaction between aluminum and germanium. When the entire surface of the substrate is covered by this Ge layer, the device is formed on this layer. If necessary, part of the Ge layer may also be removed, and optionally part of the aluminum layer may be removed.

[0089] This layer is generally deposited before the bonding step.

[0090] Preferably, the wetting layer 130 is a metal layer. Advantageously, the wetting layer is made of W, Ti, Al, Au or Cu.

[0091] According to a very advantageous embodiment, the wetting layer 130 is a metal layer, the first side of the first substrate 111 is made of a dielectric material, a semiconductor material or a metal nitride, and the first side of the second substrate 112 is made of a dielectric material, a semiconductor material or a metal nitride.

[0092] The wettability of the eutectic alloy on the wetting layer 130 is better than that on the first side of the first substrate 111 or the first side of the second substrate 112. Therefore, the eutectic alloy remains on the wetting layer 130 instead of flowing onto the substrate.

[0093] "The wettability of the eutectic alloy is better" means that the contact angle of the eutectic alloy droplet on the first side of the first substrate 111 or the first side of the second substrate 112 is at least 20° larger than the contact angle of the eutectic alloy droplet on the wetting layer 130, preferably at least 40° larger.

[0094] For example, the contact angle of an AlGe droplet on a surface made of SiO2 is greater than 110° (refer to the paper by V. Lumineau). Therefore, silicon dioxide is not wetted by the Al-Ge eutectic alloy. Therefore, it is preferable to select a wetting layer 130 such that the contact angle of the AlGe droplet on the wetting layer 130 is less than or equal to 90°, preferably less than or equal to 70°.

[0095] To determine the contact angle of the droplets of the eutectic alloy, the method used is, for example, the method described in the paper by V. Lumineau. The measurement of the contact angle is carried out by placing a droplet: observing the shape of the droplet of the eutectic alloy formed on a plane at a temperature above its melting point. For this purpose, the alloy is placed in a crucible made of alumina, with a capillary tube with a diameter of 0.6 mm at the end of the crucible. After melting is complete and the experimental temperature is reached, the piston allows a droplet to form at the end of the capillary tube. Then the crucible is lowered onto the solid surface to be studied and the droplet is deposited. At a certain temperature, on-site observation is carried out using a camera (25 images / second) through a window. Subsequently, the video recording of the droplet spreading can be used to measure and calculate the intrinsic parameters of the droplet by Drop Shape Analysis software. The pumping system can achieve a vacuum of up to 5.10 -7 mbar (or 5.10 -5 Pa).

[0096] The wetting layer 130 can be arranged according to various configurations.

[0097] The wetting layer 130 can be arranged between the first substrate 111 and the first solder ball 121 ( Figure 4A and Figure 4B ), and / or between the second substrate 112 and the second solder ball 122 ( Figure 3A and Figure 3B ).

[0098] The wetting layer 130 protrudes from the solder balls 121, 122, thus forming a free surface to accommodate the cast part 123'. The wetting layer 130 can protrude on either side of the solder balls 121 and 122. Alternatively, it can also protrude only on one side of the solder balls 121 and 122. The overflow area of the wetting layer 130 can be between dozens of nanometers and hundreds of micrometers.

[0099] The wetting layer 130 can protrude on either side of the solder balls 121, 122 covering it ( Figure 3A and Figure 3B , Figure 4A and Figure 4B ).

[0100] Alternatively, the wetting layer can also protrude only from one side of the solder ball ( Figure 5A and Figure 5B , Figure 6A and Figure 6B , Figure 7 ). Advantageously, the wetting layer 130 only protrudes outside the cavity formed by the sealing solder ball 123 and the two substrates, so as to guide the cast part 123' of the eutectic alloy out of the cavity containing the chip microelectronic devices and protect these chip microelectronic devices.

[0101] According to another alternative embodiment, the wetting layer 130 may be provided beside the sealing beads 121, 122 ( Figure 8A and Figure 8B , Figure 9 ). It may be in contact with the sealing beads 121, 122 or may be away from the sealing beads 121, 122 (i.e., the wetting layer does not contact the sealing beads). For example, the wetting layer 130 forms a band surrounding the sealing beads. The lateral member (or "bridge") may facilitate the evacuation of the cast portion towards the wetting layer. The lateral member may be made of the same or different material as the wetting layer. Preferably, the wetting layer 130 is only located outside the sealing beads (i.e., outside the cavity) and is spaced apart from the sealing beads.

[0102] The single wetting layer 130 is described above. A wetting layer may also be provided on each of the substrates 111, 112.

[0103] Alternatively, both the first substrate 111 and the second substrate 112 are locally covered by the wetting layer 130, so that during step c), the cast portion 123' of the eutectic alloy is formed on the wetting layer 130 and is at least partially, preferably completely, contained in these layers.

[0104] Using two wetting layers can better confine the eutectic material, making it more stable. This configuration can also reduce the size of these layers compared to a single wetting layer, which is particularly advantageous for the miniaturization of the device.

[0105] These two layers may be provided on the respective substrates in the same or different ways.

[0106] The size of the wetting layer 130 is determined according to the size of the beads. The size of the wetting layer 130 is selected to be able to accommodate the cast portion.

[0107] During step c), the two beads 121, 122, and even the two substrates 111, 112 are brought into close contact and then heat-treated. This treatment may be carried out in a controlled atmosphere (vacuum, inert atmosphere), and / or mechanical pressure is applied to contact the entire surface. For example, a force greater than or equal to 2 kN, 10 kN or even 30 kN may be applied.

[0108] The temperature is selected according to the eutectic alloy. The selected temperature should reach and even exceed the melting point of the eutectic alloy in order to form a solder containing the eutectic alloy between the substrates 111 and 112 to be assembled. Preferably, the applied temperature is lower than the melting point of the first bead 121 and the melting point of the second bead 122. For example, in order to produce the eutectic alloy Al-Ge, the applied temperature should be higher than 425 °C (the melting point of the eutectic alloy).

[0109] The hermetic bead 123 is made of a eutectic alloy that contains two elements, one from the first element of the first bead and the other from the second element of the second bead. This alloy is also known as solder.

[0110] The formation of the bead 123 made of the eutectic alloy ensures that the seal has a high mechanical strength.

[0111] The width of the hermetic bead 123 is, for example, between 30 μm and 200 μm. This width is chosen to be large enough to ensure good sealing while being small enough to support miniaturization.

[0112] The sum of the thicknesses of the first material and the second material is generally between 100 nm and 10 μm, preferably 1 μm.

[0113] The use of the wetting layer can be combined with the use of mechanical stoppers described in the prior art.

[0114] The above method can produce components with a thickness less than 10 μm. In addition, compared with thermocompression sealing, this seal has almost no pore-like defects at the interface, which is crucial for components that require a controlled atmosphere.

Claims

1. A method for eutectic sealing of two substrates (111, 112), the method comprising the following steps: a) Providing a first substrate (111) having a first face covered by a first solder ball (121) made of a first material and optionally covered 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 solder ball (122) made of a second material and optionally covered 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) Placing the first solder ball (121) and the second solder ball (122) in contact and performing a heat treatment to form a eutectic phase alloying the first element of the first solder ball (121) with the second element of the second solder ball (122), thereby forming a sealing solder ball (123) comprising the eutectic alloy, and sealing the first substrate (111) to the second substrate (112), the formation of the eutectic phase being accompanied by the formation of a cast portion (123') of the eutectic alloy. The method is characterized in that at least one of the first substrate (111) and the second substrate (112) is locally covered by a wetting layer (130), the contact angle of a droplet of the eutectic alloy on the wetting layer (130) being at least 20°, preferably at least 40°, smaller than the contact angle of the eutectic alloy on the first face of the first substrate (111), and the contact angle of a droplet of the eutectic alloy on the wetting layer (130) being at least 20°, preferably at least 40°, smaller than the contact angle of the eutectic alloy on the first face of the second substrate (112), whereby during step c), the cast portion (123') of the eutectic alloy is formed on the wetting layer (130).

2. The method according to claim 1, wherein The first solder ball (121) comprises the first material and the second material, the first solder ball (121) being, for example, in a multilayer form, and / or the second solder ball (122) comprises the first material and the second material, the second solder ball (122) being, for example, in a multilayer form.

3. The method according to any one of claims 1 to 2, characterized in that, The wetting layer (130) is a metal layer, preferably selected from W, Ti, Al, Au and Cu, or a metal nitride layer, such as a TiN, AlN or WN layer.

4. The 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 made of SiO2 or made of Si3N4, made of a semiconductor material or made of a metal nitride, and / or the first face of the second substrate (112) is made of a dielectric material, preferably made of SiO2 or made of Si3N4, made of a semiconductor material or made of a metal nitride.

5. The method according to any one of the preceding claims, characterized in that, The eutectic alloy is selected from Al-Ge, Au-In, Au-Sn, Au-Si, Bi-Sn and Au-Ge.

6. The method according to the preceding claim, characterized in that, For the eutectic alloy AlGe, the first material is selected from AlSi or AlCu; for the eutectic alloys Au-In, Au-Sn or Au-Si, the first material is selected from Au; and / or for the eutectic alloy Al-Ge, the second material is selected from Ge; for the eutectic alloys Au-Sn or Bi-Sn, the second material is selected from Sn; for the eutectic alloy Au-Si, the second material is selected from Si.

7. The method according to any one of claims 1 to 6, characterized in that The first solder ball (121) is disposed on the wetting layer (130), and the wetting layer (130) protrudes on either side of the first solder ball (121) or on both sides of the first solder ball (121), or the second solder ball (122) is disposed on the wetting layer (130), and the wetting layer (130) protrudes on either side of the second solder ball (122) or on both sides of the second solder ball (122).

8. The method according to any one of claims 1 to 6, characterized in that The wetting layer (130) is offset relative to the first solder ball (121) or relative to the second solder ball (122), and the wetting layer (130) is connected to the first solder ball (121) or the second solder ball (122) by a lateral member.

9. A device, comprising a first substrate (111) and a second substrate (112), the first substrate (111) and the second substrate (112) being sealed to each other by a sealing solder ball (123) containing a eutectic alloy, at least one of the first substrate (111) and the second substrate (112) being partially covered by a wetting layer (130), the contact angle of the droplets of the eutectic alloy on the wetting layer (130) being smaller than the contact angle of the eutectic alloy on the first surface of the first substrate (111), the contact angle of the droplets of the eutectic alloy on the wetting layer (130) being smaller than the contact angle of the eutectic alloy on the first surface of the second substrate (112), and a cast portion (123') of the eutectic alloy being disposed on the wetting layer (130).

10. The device according to claim 9, characterized in that, The wetting layer (130) is a metal layer, preferably selected from W, Ti, Al, Au and Cu, or a layer made of a metal nitride, such as a TiN, AlN or WN layer, and wherein the first surface of the first substrate (111) is made of a dielectric material, preferably made of SiO2 or made of Si3N4, made of a semiconductor material or made of a metal nitride, and / or wherein the first surface of the second substrate (112) is made of a dielectric material, preferably made of SiO2 or made of Si3N4, or made of a semiconductor material or made of a metal nitride.

11. The device according to any one of claims 9 to 10, characterized in that, The eutectic alloy is selected from Al-Ge, Au-In, Au-Sn, Au-Si, Bi-Sn and Au-Ge.

12. The device according to any one of claims 9 to 11, characterized in that, The sealing solder ball (123) is disposed on the wetting layer (130), and the wetting layer (130) protrudes on either side of the sealing solder ball (123) or on both sides of the sealing solder ball (123).

13. The device according to any one of claims 9 to 11, characterized in that The wetting layer (130) is locally offset relative to the sealing solder ball (123), and the wetting layer (130) is connected to the sealing solder ball (123) by a lateral member.

Images