Method for bonding microstructure elements and microstructure assemblies

Abstract

The invention relates to a method for bonding (14) microstructure elements and a microstructure assembly (64) comprising microstructure elements (10, 12).

Description

The invention relates to a method for bonding microstructure elements according to claim 1.Prior ArtIn the production of microelectromechanical devices (MEMS devices), wafer bonding is a known method in which a plurality of wafers are mechanically connected at a defined distance, wherein often electrically insulated contacts must be produced simultaneously between the structures on the different wafers.There are various known methods of wafer bonding, which are selected according to requirements and materials. One of the most common methods is anodic bonding, in which a silicon wafer is connected to a glass wafer using heat and an electric voltage. This process allows for strong chemical bonding.Another widely used method is direct bonding. Here, the surfaces of the wafers are bonded at a molecular level by temperature and pressure. This method requires enormous clean and smooth surfaces, but offers high mechanical strength. Hybrid direct bonding extends direct bonding by simultaneously bonding electrically conductive and insulating layers together.Eutectic bonding uses an alloy that is placed between the wafers and melts at a certain temperature to form the bond.In addition, there is the thermoplastically bonded bonding, by means of which materials, typically metals such as gold or copper, are bonded to one another by the application of heat and pressure.Disclosure of the InventionAccording to the present invention, a method of bonding is provided having the features of claim 1. As a result, the microstructure elements can be connected at more precise distances and with the smallest possible offset with respect to one another. Furthermore, electrical contacts which are insulated from one another can be produced between structures on both microstructure elements.The first and / or second microstructure element may comprise a substrate. The substrate can comprise at least silicon or be constructed from silicon. The substrate can have, in particular on a substrate surface, at least one coating, in particular a passivation layer, preferably formed from silicon dioxide.The first and / or second microstructure element can be a micro-optical, microelectronic, micromechanical or microelectromechanical structure element. The microstructure element may be a semiconductor device.The first and / or third bonding area can be formed by a substrate surface of the substrate and / or a coating surface of the coating.The second and / or fourth bonding surface can be a material surface of a material applied to the substrate or the coating or of a further coating applied to the substrate or the coating. The second and / or fourth bonding area can have at least one diffusion barrier with respect to the substrate. This can reduce adverse effects on the substrate during the second joining step.The first, second, third and / or fourth bonding surface may consist at least partially of silicon dioxide, silicon, aluminum, germanium, gold, silicon carbide, aluminum oxide and / or copper.The first and / or second joint pair can be electrically insulating or electrically conductive. If the first joint pair is electrically conductive, the second joint pair can be electrically insulating or vice versa.With the first joining step, the first and second microstructure elements can be mutually fixed via the first joint pair. The first joining step may include direct bonding. As a result, the first and second microstructure elements can be mechanically fixed and connected to one another. The direct bonding may be performed between a silicon dioxide surface and a silicon surface. As a result, electrical insulation between the first and second microstructure elements can be retained even after the first joining step. In the first joining step, the first and third bonding surfaces may be in contact with each other.The second joining step can comprise a thermoplastically compressive bonding, in particular between two aluminum surfaces, a eutectic bonding, in particular between an aluminum surface and a germanium surface, or a fusible connection, in particular between two aluminum surfaces. As a result, an electrically conductive connection can be produced via the second joint pair.In a preferred embodiment of the invention, it is advantageous if the alignment comprises an axial bringing together up to a mechanical contact between the first and third bonding surfaces. Further, the aligning may include aligning in at least one direction of the plane having the axial direction as normal. In the case of a mechanical contact between the first and third bonding surfaces, the second and fourth bonding surfaces can also be in mechanical contact with one another.In an advantageous embodiment of the invention, it is provided that during the axial bringing together, the second and fourth bonding surfaces touch one another temporally before a mechanical contact between the first and third bonding surfaces. At the time of the mechanical contact between the second and fourth bonding surfaces, the first and third bonding surfaces are in particular still spaced apart from one another.A preferred embodiment of the invention is advantageous in which, after the alignment and immediately before the first joining step, the second and fourth bonding surfaces are free of contact with one another, while the first and third bonding surfaces touch one another. The second and fourth bonding surfaces can be spaced apart from one another after the first joining step and before the second joining step.The first and third bonding surfaces as well as the second and fourth bonding surfaces may contact each other after the alignment and immediately before the first joining step.In a preferred embodiment of the invention, it is advantageous if the second bonding surface on the first microstructure element and / or the fourth bonding surface on the second microstructure element is accommodated axially elastically. The second and / or fourth bonding surface can be accommodated on the substrate by at least one spring element. The spring element can comprise a membrane and / or a bending beam. After the first joining step and before the second joining step, an axial distance between the third and fourth bonding surfaces may be different from an axial distance before the first joining step.In a special embodiment of the invention, it is advantageous if the first and second bonding surfaces on the first microstructure element and / or the third and fourth bonding surfaces on the second microstructure element are arranged axially offset from one another. The first and second bonding surfaces or the third and fourth bonding surfaces can also be arranged axially on a common plane. However, if the first and second bonding surfaces are arranged axially on a common plane, the second and fourth bonding surfaces are arranged axially offset from one another and vice versa.A preferred embodiment of the invention is advantageous in which the second bonding surface is arranged offset or protruding axially with respect to the first bonding surface and / or the fourth bonding surface is arranged offset or protruding axially with respect to the third bonding surface. Preferably, the second bonding surface is arranged so as to project axially with respect to the first bonding surface and the fourth bonding surface is arranged so as to project axially with respect to the third bonding surface. Furthermore, the second bonding surface is preferably arranged so as to project axially with respect to the first bonding surface and the fourth bonding surface is arranged so as to be offset axially with respect to the third bonding surface.In a preferred embodiment of the invention, it is advantageous if the second temperature is higher than the first temperature. The first temperature can be less than 220° C., in particular in the region of room temperature.The second temperature may be higher than a melting temperature, solidus temperature and / or liquidus temperature of a material forming the second and / or fourth bonding surface. The second temperature can be greater than 350° C., preferably greater than 650° C.The second temperature can be applied in a spatially restricted manner to the region or a surrounding region of the second and / or fourth bonding area. The microstructure element can have the second temperature in the second joining step only in regions. The thermal energy for applying the second temperature may be introduced by laser energy.In a specific embodiment of the invention, it is advantageous if the first microstructure element is structured on a surface facing the second microstructure element and / or the second microstructure element is structured on a surface facing the first microstructure element. The first and / or second microstructure element can have at least one indentation, a conductor track and / or a functional layer, for example a passivation region. The indentation may form a cavity between the first and second microstructure elements after bonding.According to the present invention, there is further provided a microstructure assembly having the features of claim 10. The microstructure assembly may be associated with a microelectromechanical sensor and / or actuator. The microstructure assembly may be associated with a loudspeaker.Further advantages and advantageous embodiments of the invention result from the description of the figures and the figures.DESCRIPTION OF THE FIGURESThe invention will be described in detail below with reference to the drawings. They show in detail: FIG. 1 : A method for bonding two microstructure elements in a specific embodiment of the invention. FIG. 2 : Further steps of the method from FIG. 1. FIG. 3 : A method for bonding two microstructure elements in a further specific embodiment of the invention. FIG. 4 : A method for bonding two microstructure elements in a further specific embodiment of the invention. FIG. 5 : Further steps of the method from FIG. 4. FIG. 6 : A method for bonding two microstructure elements in a further specific embodiment of the invention. FIG. 7 : Further steps of the method from FIG. 6. FIG. 8 : shows a microstructure assembly in a further specific embodiment of the invention.FIG. 1 illustrates a method of bonding two microstructure elements in a particular embodiment of the invention. FIG. 1 a) shows a plan view of a first microstructure element 10, FIG. 1 c) shows a second microstructure element 12 and FIG. 1 b) shows a cross section of the first microstructure element 10 and a cross section of the second microstructure element 12.The method for bonding 14 the first and second microstructure elements 10, 12 comprises providing 16 the first microstructure element 10 having at least one first bonding surface 18 and one second bonding surface 20 and the second microstructure element 12 structurally separate from the first microstructure element 10 and having at least one third bonding surface 22 and one fourth bonding surface 24.The first microstructure element 10 comprises a substrate 28, preferably made of silicon, on which a passivation layer 30 made of silicon dioxide is applied. The surface of the passivation layer 30 forms the first bonding area 18. The material surface of the material 32 forms the second bonding surface 20. The second bonding surface 20 is spaced apart axially from the first bonding surface 18 by an axial distance d 1 and is designed to project axially in the direction of the second microstructure element 12.The second microstructure element 12 also comprises a substrate 28, preferably made of silicon, wherein the substrate surface forms the third bonding area 22. The substrate surface facing the first microstructure element 10 is structured and has at least one indentation 34. Furthermore, a material 36, in particular germanium, is applied in regions on the substrate surface. The material surface of the material 36 forms the fourth bonding surface 24. the third and fourth bonding surfaces 22, 24 on the second microstructure element 12 are arranged axially offset from one another. The fourth bonding surface 24 is arranged axially spaced apart from the third bonding surface 22 by an axial distance d 2.The fourth bonding surface 24 is preferably completely surrounded by an indentation 38, which projects so deeply into the substrate 28 that a remaining substrate thickness 40 in the region of the indentation 38 is dimensioned such that the substrate part 42, on which the fourth bonding surface 24 is arranged, can deflect in the axial direction 26 upon application of force. The fourth bonding surface 24 is thus axially elastically received on the second microstructure element 12 by a membrane 44 on the substrate 28.As shown in FIG. 1 b), the first and second microstructure elements 10, 12 are aligned 46 with one another for bonding a first joint pair 48 formed by the first bonding surface 18 and the third bonding surface 22 opposite one another in the axial direction 26 and a second joint pair 50 formed by the second bonding surface 20 and the fourth bonding surface 24 opposite one another in the axial direction 26, 22 of the first joint pair 48 At the time of mechanical contact between the second and fourth bonding surfaces 20, 24, the first and third bonding surfaces 18, 22 are still spaced apart from each other.FIG. 2 shows further steps of the method from FIG. 1. In FIG. 2 a), the first and second microstructure elements 10, 12 are shown after the alignment and in a first joining step. In this case, the first and second bonding areas 18, 20 and the third and fourth bonding areas 22, 24 are each axially spaced apart from one another. The fourth bonding surface 24 is deflected axially away from the first microstructure element 10 by the action of force and the elastic receptacle via the membrane 44 and, in the first joining step and also after the first joining step, has an axial distance d2' from the third bonding surface 22, which deviates from the axial distance shown in FIG. 1 b) between the third and fourth bonding surfaces 22, 24 before the first joining step.The first joining step 60 takes place with the first and second microstructure elements 10, 12 aligned in this way, with which the first pair of joints 48, i.e. the first and third bonding surfaces 18, 22, is bonded at a first temperature. The connection can be effected here by direct bonding.FIG. 2 b) shows a second joining step 62, which follows in time and by means of which the second and fourth bonding surfaces 20, 24 are bonded to one another at a second temperature. The second joining step 62 can be effected here by eutectic bonding between the aluminum surface and the germanium surface. After the second joining step 62, the second and fourth bonding surfaces 20, 24 and the first and second microstructure elements 10, 12 are also connected to one another as a microstructure assembly 64, in particular are connected to one another in a substantially materially bonded manner and are no longer only in contact or pressed together.FIG. 3 shows a method for bonding two microstructure elements in a further specific embodiment of the invention. The first and second microstructure elements 10, 12 and method are similar to that of FIG. 1, the description of which is incorporated herein by reference, but with the following differences. The fourth bonding surface 24 is a material surface of a material 36 on the substrate surface of the substrate 28 of the second microstructure element 12.Formed axially below the material 36 is an indentation 66 in the region of the material 36, by means of which the fourth bonding surface 24 is accommodated axially elastically by a membrane 44 in the substrate 28 on the second microstructure element 12.FIG. 4 shows a method for bonding two microstructure elements in a further specific embodiment of the invention. The first and second microstructure elements 10, 12 and method are similar to that of FIG. 1, the description of which is incorporated herein by reference, but with the following differences. The fourth bonding surface 24 is arranged offset back axially from the third bonding surface 22 by an axial distance d 2. The fourth bonding area 24 is a material surface of a material 36, in particular aluminum. The material 36 is received in an indentation 68 in the substrate 28.FIG. 5 shows further steps of the method from FIG. 4 The method steps are the same as those from FIG. 2, the description of which is hereby incorporated, but the following differences are present. As shown in FIG. 5 a), after the alignment and in the first joining step 60, the second and fourth bonding surfaces 20, 24 of the second pair of joints 50 are free of contact with one another and have an axial distance d 3 from one another, while the first and third bonding surfaces 18, 22 of the second pair of joints 48 contact one another.FIG. 5 b) shows a second joining step 62, which follows in time and by means of which the second and fourth bonding surfaces 20, 24 are joined to one another at a second temperature and thereby join one another.FIG. 6 shows a method for bonding two microstructure elements in a further specific embodiment of the invention. The first and second microstructure elements 10, 12 and method are similar to that of FIG. 1, the description of which is incorporated herein by reference, but with the following differences. The fourth bonding surface 24 is axially recessed with respect to the third bonding surface 22 by an axial distance d 2.On a surface 72 facing away from the first microstructure element 10, the second microstructure element 12 has an elevation 74 in the region spanned by the fourth bonding surface 24. The elevation 74 can already be implemented before the first joining step or alternatively be applied after the first joining step and before the second joining step. This elevation 74 serves to move the fourth bonding surface 24 after the first joining step by surface pressing of the surface 72 over the elevation 74 axially in the direction of the first microstructure element 10 up to a mechanical contact with the second bonding surface 20.FIG. 7 shows further steps of the method from FIG. 6, the method steps being similar to those from FIG. 2, the description of which is hereby incorporated, but the following differences are present. As shown in FIG. 7 a), after the alignment and in the first joining step 60, the second and fourth bonding surfaces 20, 24 are free of contact with one another and have a distance d 3 from one another while the first and third bonding surfaces 18, 22 contact one another.FIG. 7 b) shows a second joining step 62, which follows in time and by means of which the second and fourth bonding surfaces 20, 24 of the second pair of joints 50 are bonded to one another at a second temperature and are joined together in the process.FIG. 8 shows a microstructure assembly in another specific embodiment of the invention. Microstructure assembly 64 is comparable to that of FIG. 2 a) except for the following differences. Microstructure assembly 64 is shown after alignment of first and second microstructure elements 10, 12 and at first joining step 60. The second bonding surface 20 is axially spaced apart from the first bonding surface 18 by an axial distance d 1. The second bonding surface is recessed. The fourth bonding surface 24 is axially spaced apart from the third bonding surface 22 by an axial distance d 2 and is configured to be axially recessed with respect to the third bonding surface. An axial distance provided by the mechanical contact between the first and third bonding surfaces 18, 22 is zero and is different from an axial distance d 3 of the second and fourth bonding surfaces 20, 24.

Claims

Method for bonding (14) microstructure elements, comprising the steps of providing (16) a first microstructure element (10) having at least one first and second bonding surface (18, 20) and a second microstructure element (12), structurally separate from the first microstructure element (10), having at least one third and fourth bonding surface (22, 24), aligning (46) the first and second microstructure elements (10, 12) with one another for the subsequent bonding of a first joining pair (48) formed by the first bonding surface (18) and the third bonding surface (22) opposite one another in the axial direction (26) and of a second joining pair (50) formed by the second bonding surface (22) and the fourth bonding surface (24) opposite one another in the axial direction (26), subsequently a first joining step (60), with which the first and third bonding surfaces (18, 22) are bonded to one another at a first temperature, a second joining step (62) following one another in time, with which the second and fourth bonding surfaces (20, 24) are bonded to one another at a second temperature, wherein the first and second bonding surfaces (18, 20) are axially spaced apart from one another by an axial distance (d1), the third and fourth bonding surfaces (22, 24) are axially spaced apart from one another by an axial distance (d2) and / or after the first joining step (60) and before the second joining step (62) the second and fourth bonding surfaces (20, 24) are axially spaced apart from one another by an axial distance (d3).The bonding method (14) according to claim 1, characterized in that the aligning (46) comprises an axial bringing together (54) up to a mechanical contact between the first and third bonding surfaces (18, 22).Method for bonding (14) according to Claim 2, characterized in that during the axial bringing together (54) the second and fourth bonding surfaces (20, 24) touch one another temporally before a mechanical contact between the first and third bonding surfaces (18, 22).Method for bonding (14) according to one of the preceding claims, characterized in that after the alignment (46) and immediately before the first joining step (60), the second and fourth bonding surfaces (20, 24) are free of contact with one another, while the first and third bonding surfaces (18, 22) touch one another.Method for bonding (14) according to one of the preceding claims, characterized in that the second bonding surface (20) on the first microstructure element (10) and / or the fourth bonding surface (24) on the second microstructure element (12) is axially accommodated in an elastic manner.Method for bonding (14) according to one of the preceding claims, characterized in that the first and second bonding surfaces (18, 20) on the first microstructure element (10) and / or the third and fourth bonding surfaces (22, 24) on the second microstructure element (12) are arranged axially offset with respect to one another.Method for bonding (14) according to Claim 6, characterized in that the second bonding area (20) is arranged offset or protruding axially with respect to the first bonding area (18) and / or the fourth bonding area (24) is arranged offset or protruding axially with respect to the third bonding area (22).Bonding method (14) according to one of the preceding claims, characterized in that the second temperature is higher than the first temperature.Method for bonding (14) according to one of the preceding claims, characterized in that the first microstructure element (10) is structured on a surface (72) facing the second microstructure element (12) and / or the second microstructure element (12) is structured on a surface (72) facing the first microstructure element (10).Microstructure assembly (64) having a first microstructure element (10) having at least one first and second bonding surface (18, 20), a second microstructure element (12) having at least one third and fourth bonding surface (22, 24), wherein the first bonding surface (18) and the axially opposite third bonding surface (22) form a first joining pair (48), and the second bonding surface (20) and the axially opposite fourth bonding surface (24) form a second joining pair (50), wherein the second bonding surface (20) is accommodated axially elastically on the first microstructure element (10) and / or the fourth bonding surface (24) is accommodated axially elastically on the second microstructure element (12).

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