Method for bonding microstructure elements, and microstructure assembly

Abstract

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

Description

[0001] Method for bonding microstructure elements and microstructure assemblies

[0002] The invention relates to a method for bonding microstructure elements according to claim 1. Furthermore, the invention relates to a microstructure assembly comprising microstructure elements.

[0003] State of the art

[0004] In the manufacture of microelectromechanical components (MEMS components), wafer bonding is a well-known process in which several wafers are mechanically connected at a defined distance, often requiring the simultaneous creation of electrically isolated contacts between the structures on the different wafers.

[0005] There are various known wafer bonding processes, which are selected depending on the requirements and materials. One of the most common is anodic bonding, in which a silicon wafer is bonded to a glass wafer using heat and an electrical voltage. This process enables a strong chemical bond.

[0006] Another common process is direct bonding. This involves bonding the wafer surfaces at the molecular level using temperature and pressure. This process requires extremely clean and smooth surfaces, but offers high mechanical strength. Hybrid direct bonding extends direct bonding by simultaneously bonding electrically conductive and insulating layers.

[0007] Eutectic bonding uses an alloy that is placed between the wafers and melts at a specific temperature to form the bond.

[0008] There is also thermocompression bonding, which joins materials, typically metals such as gold or copper, together by applying heat and pressure.

[0009] Disclosure of the invention

[0010] According to the present invention, a bonding method is proposed with the features of claim 1. This allows the microstructure elements to be connected to one another at more precise spacings and with the smallest possible offset. Furthermore, mutually insulated electrical contacts can be created between structures on both microstructure elements.

[0011] The first and / or second microstructure element can comprise a substrate. The substrate can comprise at least silicon or be composed of silicon. The substrate can comprise, in particular on a substrate surface, at least one coating, in particular a passivation layer, preferably formed from silicon dioxide.

[0012] The first and / or second microstructure element may be a micro-optical, microelectronic, micromechanical, or microelectromechanical structural element. The microstructure element may be a semiconductor component.

[0013] The first and / or third bonding surface may be formed by a substrate surface of the substrate and / or a coating surface of the coating.

[0014] 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 surface can have at least one diffusion barrier to the substrate. This can reduce adverse effects on the substrate during the second joining step.

[0015] 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.

[0016] The first and / or second joining pair can be electrically insulating or electrically conductive. If the first joining pair is electrically conductive, the second joining pair can be electrically insulating, or vice versa.

[0017] During the first joining step, the first and second microstructure elements can be mutually secured via the first joining pair. The first joining step can comprise direct bonding. This allows the first and second microstructure elements to be mechanically secured and connected to one another. The direct bonding can occur between a silicon dioxide surface and a silicon surface. This allows electrical insulation between the first and second microstructure elements to be maintained even after the first joining step. During the first joining step, the first and third bonding surfaces can be in contact with one another. The second joining step can comprise thermocompression bonding, in particular between two aluminum surfaces, eutectic bonding, in particular between an aluminum surface and a germanium surface, or a fused bond, in particular between two aluminum surfaces.This allows an electrically conductive connection to be established via the second joining pair.

[0018] In a preferred embodiment of the invention, it is advantageous if the alignment comprises axially bringing the first and third bonding surfaces together until mechanical contact is established. Furthermore, the alignment may include alignment in at least one direction of the plane having the axial direction as the normal. With mechanical contact between the first and third bonding surfaces, the second and fourth bonding surfaces may also be in mechanical contact with each other.

[0019] In an advantageous embodiment of the invention, it is provided that during the axial joining, the second and fourth bonding surfaces touch each other prior to any mechanical contact between the first and third bonding surfaces. At the time of mechanical contact between the second and fourth bonding surfaces, the first and third bonding surfaces are, in particular, still spaced apart from each other.

[0020] A preferred embodiment of the invention is advantageous in which, after alignment and immediately before the first joining step, the second and fourth bonding surfaces are contact-free, while the first and third bonding surfaces are in contact. The second and fourth bonding surfaces can be spaced apart from each other after the first joining step and before the second joining step.

[0021] The first and third bonding surfaces as well as the second and fourth bonding surfaces can touch each other after alignment and immediately before the first joining step.

[0022] In a preferred embodiment of the invention, it is advantageous if the second bonding surface is axially elastically supported on the first microstructure element and / or the fourth bonding surface is axially elastically supported on the second microstructure element. The second and / or fourth bonding surface can be supported 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 can be different from an axial distance before the first joining step.

[0023] In a specific 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.

[0024] A preferred embodiment of the invention is advantageous in which the second bonding surface is arranged axially recessed or axially protruding relative to the first bonding surface and / or the fourth bonding surface is arranged axially recessed or axially protruding relative to the third bonding surface. Preferably, the second bonding surface is arranged axially protruding relative to the first bonding surface, and the fourth bonding surface is arranged axially protruding relative to the third bonding surface. Furthermore, the second bonding surface is arranged axially protruding relative to the first bonding surface, and the fourth bonding surface is arranged axially recessed relative to the third bonding surface.

[0025] 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 range of room temperature.

[0026] 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.

[0027] The second temperature may be greater than 350°C, preferably greater than 650°C.

[0028] The second temperature can be applied in a spatially limited manner to the area or a surrounding area of ​​the second and / or fourth bonding surface. The microstructure element can only have the second temperature in certain areas during the second joining step. The heat energy for applying the second temperature can be introduced by laser energy.

[0029] 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 can form a cavity between the first and second microstructure elements after bonding.

[0030] According to the present invention, a microstructure assembly with the features of claim 10 is further proposed. The microstructure assembly can be associated with a microelectromechanical sensor and / or actuator. The microstructure assembly can be associated with a loudspeaker. Further advantages and advantageous embodiments of the invention will become apparent from the description of the figures and the illustrations.

[0031] Character description

[0032] The invention is described in detail below with reference to the figures. They show in detail:

[0033] Figure 1: A method for bonding two microstructure elements in a specific embodiment of the invention.

[0034] Figure 2: Further steps of the process from Figure 1.

[0035] Figure 3: A method for bonding two microstructure elements in another specific embodiment of the invention.

[0036] Figure 4: A method for bonding two microstructure elements in another specific embodiment of the invention.

[0037] Figure 5: Further steps of the process from Figure 4.

[0038] Figure 6: A method for bonding two microstructure elements in another specific embodiment of the invention.

[0039] Figure 7: Further steps of the process from Figure 6.

[0040] Figure 8: A microstructure assembly in another specific embodiment of the invention.

[0041] Figure 1 shows a method for bonding two microstructure elements in a specific embodiment of the invention. Figure 1 a) shows a plan view of a first microstructure element 10, Figure 1 c) shows a second microstructure element 12, and Figure 1 b) shows a cross-section of the first microstructure element 10 and a cross-section of the second microstructure element 12.

[0042] The method for bonding 14 the first and second microstructure elements 10, 12 comprises providing 16 the first microstructure element 10 with at least a first bonding surface 18 and a second bonding surface 20 and the second microstructure element 12, which is structurally separate from the first microstructure element 10, with at least a third bonding surface 22 and a fourth bonding surface 24. The first and second microstructure elements 10, 12 are arranged opposite one another in the axial direction 26.

[0043] 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 surface 18. A material 32, preferably aluminum, is applied to the passivation layer 30 in some regions. The material surface of the material 32 forms the second bonding surface 20. The first and second bonding surfaces 18, 20 on the first microstructure element 10 are arranged axially offset from one another. The second bonding surface 20 is axially spaced from the first bonding surface 18 by an axial distance d1 and is designed to project axially toward the second microstructure element 12.

[0044] The second microstructure element 12 also comprises a substrate 28, preferably made of silicon, wherein the substrate surface forms the third bonding surface 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 to the substrate surface in certain regions. 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 from the third bonding surface 22 by an axial distance d2.

[0045] 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 when force is applied.

[0046] The fourth bonding surface 24 is thus axially elastically supported on the second microstructure element 12 by a membrane 44 on the substrate 28.

[0047] As shown in Figure 1 b), an alignment 46 of the first and second microstructure elements 10, 12 to one another takes place for bonding a first joining pair 48 formed by the first bonding surface 18 and the third bonding surface 22 opposite in the axial direction 26, and a second joining pair 50 formed by the second bonding surface 20 and the fourth bonding surface 24 opposite in the axial direction 26. The alignment 46 comprises, in particular, on the one hand, an alignment 46 in at least one direction 52 of the plane 53 having the axial direction 26 as the normal, and an axial bringing together 54 until a mechanical contact between the first and third bonding surfaces 18, 22 occurs.During the axial joining 54, as shown here with the first microstructure element 10 drawn in dashed lines, the second and fourth bonding surfaces 20, 24 of the second joining pair 50 touch each other prior to a mechanical contact between the first and third bonding surfaces 18, 22 of the first joining pair 48. At the time of the 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.

[0048] Figure 2 shows further steps of the method from Figure 1. Figure 2 a) shows the first and second microstructure elements 10, 12 after alignment and during a first joining step. The first and second bonding surfaces 18, 20 and the third and fourth bonding surfaces 22, 24 are each axially spaced 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 absorption via the membrane 44 and has an axial distance d2' from the third bonding surface 22 during the first joining step and also after the first joining step, which deviates from the axial distance between the third and fourth bonding surfaces 22, 24 shown in Figure 1 b) before the first joining step.

[0049] With the first and second microstructure elements 10, 12 aligned in this way, the first joining step 60 is performed, with which the first joining pair 48, i.e., the first and third bonding surfaces 18, 22, are bonded at a first temperature. The connection can be made by direct bonding.

[0050] Figure 2 b) shows a subsequent second joining step 62, in which the second and fourth bonding surfaces 20, 24 are bonded together at a second temperature. The second joining step 62 can be performed 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 bonded together as a microstructure assembly 64, in particular, they are essentially bonded together in a materially bonded manner and no longer merely in contact or pressed together.

[0051] Figure 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 the method are similar to those in Figure 1, the description of which is hereby incorporated herein, 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. The material 36 is, in particular, aluminum. Axially below the material 36, an indentation 66 is formed in the region of the material 36, through which the fourth bonding surface 24 is axially elastically held on the second microstructure element 12 by a membrane 44 in the substrate 28.

[0052] Figure 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 the method are similar to those in Figure 1, the description of which is hereby incorporated herein, but with the following differences. The fourth bonding surface 24 is arranged axially offset from the third bonding surface 22 by an axial distance d2. The fourth bonding surface 24 is a material surface of a material 36, in particular aluminum. The material 36 is received in a recess 68 in the substrate 28.

[0053] Figure 5 shows further steps of the method from Figure 4. The method steps are similar to those from Figure 2, the description of which is hereby incorporated, but with the following differences. As shown in Figure 5 a), after alignment and during the first joining step 60, the second and fourth bonding surfaces 20, 24 of the second joining pair 50 are non-contacting and have an axial distance d3 from each other, while the first and third bonding surfaces 18, 22 of the second joining pair 48 are in contact.

[0054] Figure 5 b) shows a subsequent second joining step 62, with which the second and fourth bonding surfaces 20, 24 are connected to one another at a second temperature and thereby join to one another.

[0055] Figure 6 shows a method for bonding two microstructure elements in another specific embodiment of the invention. The first and second microstructure elements 10, 12 and the method are similar to those in Figure 1, the description of which is hereby incorporated herein, but with the following differences. The fourth bonding surface 24 is axially offset from the third bonding surface 22 by an axial distance d2.

[0056] On a surface 72 facing away from the first microstructure element 10, the second microstructure element 12 has a raised portion 74 in the region defined by the fourth bonding surface 24. The raised portion 74 can be formed prior to the first joining step or, alternatively, can be applied after the first joining step and prior to the second joining step. This raised portion 74 serves to move the fourth bonding surface 24 axially toward the first microstructure element 10 after the first joining step by pressing the surface 72 flat over the raised portion 74 until it makes mechanical contact with the second bonding surface 20.

[0057] Figure 7 shows further steps of the method shown in Figure 6. The method steps are similar to those shown in Figure 2, the description of which is incorporated herein, but with the following differences. As shown in Figure 7 a), after alignment and during the first joining step 60, the second and fourth bonding surfaces 20, 24 are non-contacting and are spaced apart by a distance d3, while the first and third bonding surfaces 18, 22 are in contact.

[0058] Figure 7 b) shows a subsequent second joining step 62, with which the second and fourth bonding surfaces 20, 24 of the second joining pair 50 are bonded to one another at a second temperature and thereby join to one another.

[0059] Figure 8 shows a microstructure assembly in a further specific embodiment of the invention. The microstructure assembly 64 is comparable to that in Figure 2 a) except for the following differences. The microstructure assembly 64 is shown after alignment of the first and second microstructure elements 10, 12 and during the first joining step 60. The second bonding surface 20 is axially spaced from the first bonding surface 18 by an axial distance d1. The second bonding surface is set back. The fourth bonding surface 24 is axially spaced from the third bonding surface 22 by an axial distance d2 and is set back axially from the third bonding surface. An axial distance existing due to the mechanical contact between the first and third bonding surfaces 18, 22 is zero and different from an axial distance d3 of the second and fourth bonding surfaces 20, 24.

Claims

Patent claims 1. A method for bonding (14) microstructure elements, comprising the steps of providing (16) a first microstructure element (10) with at least a first and second bonding surface (18, 20) and a second microstructure element (12) structurally separate from the first microstructure element (10) with at least a 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 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 in the axial direction (26), then 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 temporally subsequent second joining step (62) 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 spaced apart by an axial distance (d1), the third and fourth bonding surfaces (22, 24) are spaced apart 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 surface (20,24) are axially spaced from each other by an axial distance (d3)., 2. Method for bonding (14) according to claim 1, characterized in that the alignment (46) comprises an axial bringing together (54) until a mechanical contact between the first and third bonding surfaces (18, 22).

3. A method for bonding (14) according to claim 2, characterized in that during the axial joining (54) the second and fourth bonding surfaces (20, 24) touch each other prior to a mechanical contact between the first and third bonding surfaces (18, 22).

4. A method for bonding (14) according to any 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 contact-free with each other, while the first and third bonding surfaces (18, 22) are in contact.

5. A method for bonding (14) according to any one of the preceding claims, characterized in that the second bonding surface (20) is received on the first microstructure element (10) and / or the fourth bonding surface (24) is received on the second microstructure element (12) in an axially elastic manner.

6. A method for bonding (14) according to any 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 from one another.

7. The bonding method (14) according to claim 6, characterized in that the second bonding surface (20) is arranged axially set back or axially projecting relative to the first bonding surface (18) and / or the fourth bonding surface (24) is arranged axially set back or axially projecting relative to the third bonding surface (22).

8. Bonding method (14) according to one of the preceding claims, characterized in that the second temperature is higher than the first temperature.

9. Bonding method (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).

10. Microstructure assembly (64) comprising a first microstructure element (10) with at least a first and second bonding surface (18, 20), a second microstructure element (12) with at least a 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 axially elastically received on the first microstructure element (10) and / or the fourth bonding surface (24) is axially elastically received on the second microstructure element (12).

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