Micromechanical sensor device and corresponding manufacturing process

Abstract

Micromechanical sensor device with: an ASIC substrate (10) with a first front side (VSa) and a first back side (RSa); a rewiring device (20) formed on the first front side (VSa) with a plurality of stacked conductor track levels (LB0, LB1) and insulation layers (I); a MEMS substrate (9) with a second front (VS) and a second back (RS); a first micromechanical functional layer (16) formed above the second front surface (VS); a second micromechanical functional layer (17) formed above the first micromechanical functional layer (16), which is connected to the rewiring device (20) via a bond connection (50); wherein a movable sensor structure (MS) is formed in the second micromechanical functional layer (17) which is anchored on one side to the MEMS substrate (9) via a first anchoring area (17b') formed in the second micromechanical functional layer (17); wherein in the second micromechanical functional layer (17) an electrical connection element formed in a second anchoring area (17d; 17d'; 17d'') is anchored on one side via a contact area (52) of the bond connection (50) on the ASIC substrate (10); and wherein the first anchoring area (17b') and the second anchoring area (17d; 17d'; 17d'') are elastically connected to each other via a spring element (17c) formed in the second micromechanical functional layer (17).

Description

[0001] The invention relates to a micromechanical sensor device and a corresponding manufacturing process.

[0002] The subsequently published documents DE 10 2014 200 500 A1, DE 10 2014 210 945 A1 and DE 10 2014 200 512 A1 each disclose a micromechanical sensor device with an ASIC substrate and a MEMS substrate, wherein a functional layer of the MEMS substrate is connected to the front of the ASIC substrate via a bond connection and wherein a functional layer of the MEMS substrate has a movable sensor structure with anchoring areas. State of the art

[0003] Although any micromechanical components can be used, the present invention and the underlying problem are explained using silicon-based inertial sensor components.

[0004] Micromechanical sensor devices for measuring, for example, acceleration, rotation rate, magnetic field, and pressure are well-known and mass-produced for various applications in the automotive and consumer sectors. Trends in consumer electrodes include, in particular, the miniaturization of components, functional integration, and effective cost reduction.

[0005] Nowadays, acceleration and gyroscope sensors, as well as acceleration and magnetic field sensors, are already being manufactured as combination sensors (6d), and in addition, there are initial 9d modules in which 3-axis acceleration, gyroscope and magnetic field sensors are combined in a single sensor device.

[0006] Currently, the inertial sensor market is dominated by mold packages, in which silicon chips, such as a MEMS chip and an evaluation ASIC chip, are bonded to a common substrate, connected to each other and to external contacts via wire bonds, and then coated with a plastic compound. For the future miniaturization of MEMS sensor and actuator devices, so-called chip-scale packages are of great importance. These components completely eliminate the need for a plastic encapsulation. Instead, the silicon chips are soldered directly onto the application circuit boards using flip-chip technology. Such components are sometimes also referred to as bare-die assemblies. They offer advantages in terms of footprint and potentially also height compared to similar products in mold packages.

[0007] One of the major challenges of chip-scale packages for MEMS sensor devices is managing stress effects. Due to the direct flip-chip mounting of the silicon chips onto the application circuit boards, bending is generally coupled into the MEMS chip more directly and strongly than with mold packages, where the stress is mediated via adhesives and molding compound and therefore occurs in a less pronounced manner.

[0008] Methods of so-called vertical integration, hybrid integration, or 3D integration are known in which at least one MEMS wafer and one evaluation ASIC wafer are mechanically and electrically connected to each other via wafer bonding processes, for example from US 7,250,353 B2 or US 7,442,570 B2. These vertical integration methods are particularly attractive in combination with silicon through-hole vias and flip-chip technologies, which allows external contacting to be carried out as a "bare die module" or "chip scale package," i.e., without plastic packaging, as is known from US 2012 / 0049299 A1 or US 2012 / 0235251 A1.

[0009] US Patent 2013 / 0001710 A1 discloses a method and a system for forming a MEMS sensor device, wherein a handling wafer is bonded to a MEMS wafer via a dielectric layer. After structuring the MEMS wafer to form the micromechanical sensor device, a CMOS wafer is bonded to the MEMS wafer containing the sensor device. At the end of the process, the handling wafer can be further processed by etching or resurfacing, if necessary.

[0010] Fig. Figure 4 is a schematic cross-sectional view to illustrate the problem of an exemplary micromechanical sensor device.

[0011] In Fig. Reference numeral 4 (reference numeral 9) denotes a MEMS substrate, for example, a chip substrate, comprising a silicon base substrate 13, a structured first insulating layer 14 deposited thereon, a structured first micromechanical functional layer 16 deposited thereon, and a structured second insulating layer 15 deposited above it. A second micromechanical functional layer 17 is deposited and structured above the second insulating layer 15. The insulating layers 14 and 15 are, for example, made of silicon dioxide, whereas the first and second micromechanical functional layers 16 and 17 are made of polysilicon. In this example, the first, thinner micromechanical functional layer 16 made of polysilicon primarily serves as a conductor layer with conductor sections LB, while movable micromechanical sensor structures MS, e.g., for acceleration, rotation rate, or other measurements, are located in the second, thicker micromechanical functional layer 17.Magnetic sensors are formed.

[0012] The exemplary sensor structure MS is connected to the second insulation layer 15 and the first micromechanical functional layer 9 via rigid anchoring areas 17a, 17b.

[0013] The MEMS substrate 9 can contain additional micromechanical functional layers and insulating layers. The micromechanical functional layers can also be applied by wafer bonding followed by resurfacing.

[0014] Reference numeral 10 denotes an ASIC substrate with a front side VSa and a back side VSa, for example also a chip substrate, which is preferably manufactured in a CMOS process. It consists of a base silicon substrate 18, doped semiconductor layers 19 for realizing integrated electrical circuits, and a rewiring device 20, which is formed on the front side VSa of the ASIC substrate 10 and which has a plurality of stacked conductor layers LB1, LB0, contact plugs KS for electrically connecting the conductor layers LB0, LB1 as well as for external electrical connection, and a plurality of insulating layers I, which electrically insulate the conductor layers or their surroundings.

[0015] A via DK connects the front side VSA of the ASIC substrate 10 to its back side RSa. A further insulating layer 27 is deposited on the back side RSa and has embedded rewiring traces 28a, 28b, which serve for electrical contact. This electrical contact and mechanical mounting on a carrier substrate 30 is achieved using solder balls B1, B2. The carrier substrate 30 also has conductive traces 30a, 30b for electrical connection.

[0016] The MEMS substrate 9 and the ASIC substrate 10 are joined together using a metallic bonding process, e.g., a wafer bonding process, for example, via eutectic bonding of aluminum with germanium. In this process, for example, an uppermost aluminum conductor layer on the ASIC substrate 10 is used as the bonding surface, and germanium is deposited as the uppermost layer on the second micromechanical functional layer 17 of the MEMS substrate 9. The two substrates are then pressed together at temperatures above 430 °C under sufficient pressure to create a eutectic liquid phase. The AlGe (aluminum-germanium) bond 50, with the aid of a surrounding bonding frame 51, hermetically encapsulates the movable sensor structure MS in a cavity K and simultaneously enables the anchoring area 17b of the second micromechanical functional layer 17 to have an electrical contact area 52 with the ASIC substrate 10.Other metallic bonding methods, such as copper-tin bonding or thermocompressive bonding, are also conceivable in principle.

[0017] To establish a stable mechanical connection between the MEMS substrate 9 and the ASIC substrate 10, a relatively wide, circumferential bonding frame 51 is usually implemented. The movable sensor structure MS is arranged as symmetrically as possible within this bonding frame 51 to compensate for external stress effects.

[0018] The electrical contact areas 52 formed by the bond 50 are usually implemented internally as very small contacts. Since a large number of contacts are required, it is not possible to design these contacts to be very large and therefore mechanically stable.

[0019] The electrical contact areas 52 can be positioned either very close to the bonding frame 51 or in the center of the chip. When positioned close to the bonding frame, they are mechanically supported during the bonding process by their immediate proximity to the wide bonding frame 51. However, during the singulation process, usually a sawing process, the contact areas 52 are located very close to the cutting line and are subject to vibrations that can originate from there and damage the contact areas 52.

[0020] In the center of the chip, the contact areas 52 are subjected to high mechanical stress during the bonding process and can be damaged. High mechanical stress on the contacts 52 can also occur there during operation if, as in the present example, the component is soldered onto a carrier substrate 30, which can transfer stress effects to the component.

[0021] In Fig. 4. Such bending stress V leads to cracks RI in the electrical contacts 52. This type of bending stress can be caused by the load on the circuit board during pressing it into an end device or by differing coefficients of thermal expansion. In addition to damaging the contact areas 52, the contact areas 52 within the bonding frame 51 also always cause asymmetrical mechanical bending between the MEMS substrate 9 and the ASIC substrate 10. This makes the MEMS substrate very sensitive to external stress, which reduces its service life. Disclosure of the invention

[0022] The invention provides a micromechanical sensor device according to claim 1 and a corresponding manufacturing method according to claim 11.

[0023] Preferred further training courses are the subject of the respective sub-claims. Advantages of the invention

[0024] The present invention provides a micromechanical sensor device comprising a MEMS substrate with a movable sensor structure and an associated ASIC substrate, which can be used for evaluation purposes. The sensor device according to the invention includes a robust mechanical and / or electrical contact connection between the MEMS substrate and the ASIC substrate, which simultaneously reduces the stress sensitivity of the component. The sensor device is compatible with currently common manufacturing processes and can also be combined with additional measures to reduce stress sensitivity.

[0025] The idea underlying the present invention is that an electrical connection element formed in an anchoring area of ​​the micromechanical functional layer containing the sensor structure is elastically coupled to a further anchoring area in the micromechanical functional layer containing the sensor structure via a spring element.

[0026] The single-sided spring suspension prevents mechanical overload of the corresponding contact area. Significantly smaller contact areas can be implemented. The contact areas can be freely positioned within the component. Due to the spring suspension, the contact areas do not transfer stress to the MEMS substrate.

[0027] According to a preferred further development, an additional electrical contact area is formed in the first anchoring area. This can conduct electrical signals from the first micromechanical functional layer.

[0028] According to a further preferred embodiment, the second anchoring area is electrically connected to the rewiring device via the contact area. This makes it easy to input a signal into the ASIC chip.

[0029] According to a further preferred embodiment, the second anchoring area is connected to the rewiring device via an electrically insulating spacer area. This allows a capacitor plate to be formed and suitably anchored in the second micromechanical functional layer.

[0030] According to a further preferred embodiment, the electrical connection element has a perforation. This increases the effectiveness of an undercutting step.

[0031] According to a further preferred embodiment, the electrical contact area, together with a conductor track area formed in the first micromechanical functional layer, forms a measuring capacitor structure. This allows stress changes to be measured.

[0032] According to a further preferred embodiment, the electrical contact area, together with a conductor track area formed in the first micromechanical functional layer, forms a short-circuit test structure. This allows for the detection of errors during the bonding process.

[0033] According to a further preferred embodiment, a cavity is formed between the first front surface and the second front surface, wherein the first anchorage area and the second anchorage area are each bounded by the cavity on their unanchored side. This creates space for the unconnected side of the anchorage areas.

[0034] According to another preferred development, the bond connection has a circumferential bond frame area. This allows the sensor structure to be capped.

[0035] According to a further preferred embodiment, the spring element is under preload with respect to the first front face. This improves bond strength, especially in small contact areas. Brief description of the drawings

[0036] Further features and advantages of the present invention are explained below with reference to embodiments and the figures.

[0037] They show: Fig. 1 a schematic cross-sectional view to illustrate a micromechanical sensor device according to a first embodiment of the present invention; Fig. 2 a schematic cross-sectional view to illustrate a micromechanical sensor device according to a second embodiment of the present invention; Fig. 3 a schematic cross-sectional view to illustrate a micromechanical sensor device according to a third embodiment of the present invention; and Fig. 4 A schematic cross-sectional view to illustrate the problem of an exemplary micromechanical sensor device. Embodiments of the invention

[0038] In the figures, identical reference symbols denote identical or functionally equivalent elements.

[0039] Fig. Figure 1 shows a schematic cross-sectional view to illustrate a micromechanical sensor device according to a first embodiment of the present invention.

[0040] The in Fig. The first embodiment of the micromechanical sensor device according to the invention, as shown in Figure 1, differs from the exemplary sensor device according to Figure 1. Fig. 4 in the design and coupling of the second micromechanical functional layer 17.

[0041] The micromechanical functional layer 17 exhibits according to Fig. 1 like the one according to Fig. 4. A rigid anchoring area 17a is provided at the edge, which is connected to the movable sensor structure MS. Furthermore, a first anchoring area 17b' is provided in the second micromechanical functional layer 17, which is anchored on one side to the first micromechanical functional layer 16 of the MEMS substrate 9 on a conductor track area LB.

[0042] In a second anchoring area 17d, an electrical connection element is formed, which is anchored and electrically connected via a contact area 52 of the bond connection 50 on the rewiring device 20 of the ASIC substrate 10. Here, electrical signals can be introduced into the ASIC substrate 10 via the contact plugs KS and the stacked conductor track layers LB0, LB1 of the sensor structure MS of the MEMS substrate 9. The second anchoring area 17d is also anchored only on one side.

[0043] The cavity K provides sufficient free space between the first anchoring area 17b' and the second anchoring area 17d. A spring element 17c formed in the second micromechanical functional layer 17 elastically connects the first anchoring area 17b' and the second anchoring area 17d. The two spring-loaded anchoring areas 17b', 17d are arranged within the circumferential bonding frame 51 of the bonding connection 50.

[0044] Enlarged cavities or other structures can be inserted under the anchoring areas 17b', 17d during the manufacturing process, which locally increase the undercutting in these areas in order to suitably adapt the area of ​​the contact areas 52.

[0045] Otherwise, the first embodiment is according to Fig. 1 identically constructed as the exemplary sensor device described above according to Fig. 4.

[0046] Fig. Figure 2 shows a schematic cross-sectional view to illustrate a micromechanical sensor device according to a second embodiment of the present invention.

[0047] In the second embodiment according to Fig. 2 Within the second anchoring area 17d' above the contact area 52, a perforation is provided to allow suitable undercutting of the contact area 52. The size of the perforation P is chosen to be particularly narrow in the case of a eutectic AIGe bond 50, such that no bonding material can penetrate the perforation P due to surface tension. It has proven particularly advantageous to choose a perforation P narrower than 4 µm (micrometers).

[0048] In the second embodiment, an additional conductor track section LB' is provided above the second anchoring area 17d' in the first micromechanical functional layer 16. Together with the second anchoring area 17d', a short-circuit test structure can thus be formed.

[0049] This short-circuit test structure allows for electrical measurement to verify whether the eutectic bond 50 extends through the perforation P or beyond the edge of the contact area 52 and makes mechanical and electrical contact with the MEMS substrate 9. Advantageously, such a short-circuit test structure can be provided at least at one supercritical contact area 52 to ensure the function and reliability of each individual component. A supercritical contact area 52 is defined here as a contact area that either has a slightly larger perforation P, for example, larger than 5 µm, or a contact area 52 that has a slightly larger surface area, thus exhibiting a slightly higher local concentration of eutectic bond material and therefore being more prone to flow.

[0050] Furthermore, it can prove advantageous to design the spring-loaded second anchoring area 17d' with the contact area 52 in such a way that it comes into mechanical contact slightly earlier than the fixed bonding frame 51 during the bonding process and is thus always under some pressure or preload via the spring element 17c, thereby creating a very reliable bond connection in the contact area 52.

[0051] This preload and the spring suspension via the spring element 17c ensure high reliability of the contact area 52 even under high external mechanical loads. The mechanical preload can be achieved either by a layer (not shown) applied to either the ASIC substrate 10 or the MEMS substrate 9 in the contact area. Alternatively, the spring element 17c can be designed to be pre-bent. For example, an epitaxially grown polysilicon layer can be used as the second micromechanical functional layer 17. The growth conditions, doping, and post-temperature treatment are specifically tailored to create a stress gradient in the second micromechanical functional layer, causing the spring element 17c to deflect slightly away from the MEMS substrate 9.

[0052] Fig.3 a schematic cross-sectional view to illustrate a micromechanical sensor device according to a third embodiment of the present invention.

[0053] In the third embodiment, a spacer I1 is provided below the contact area 52' of the bond connection 50, below the perforated second anchoring area 17d''. The spacer I1 is integrated into the bond connection 50, so that both the bonding material and the material of the spacer I1 are present at this point.

[0054] The second anchoring area 17d'' with the perforation P and the conductor track section LB' of the first micromechanical functional layer 16 thus form a measuring capacitor structure. The capacitance of this capacitor structure allows for the measurement of changes in the distance d between the second anchoring area 17d'' and the conductor track section LB', which can be useful both during production and in later use.

[0055] During bonding, the bonding frame 51 becomes soft and compressed. Using conventional methods, such as infrared microscopy, it is very difficult to measure after bonding whether the bonding was successful, i.e., whether the components are firmly bonded to each other everywhere on the wafer. With the help of such a capacitance measurement of the measuring capacitor structure, it is easy to determine whether a deflection of the spring element 17c, and thus compression, has occurred. In field applications, the deflection can be continuously monitored using the measuring capacitor structure, which significantly improves system performance.

[0056] Although the present invention has been described with reference to preferred embodiments, it is not limited thereto. In particular, the materials and topologies mentioned are only examples and are not limited to the examples described.

Claims

[1] Micromechanical sensor device with: an ASIC substrate (10) with a first front side (VSa) and a first back side (RSa); a rewiring device (20) formed on the first front side (VSa) with a plurality of stacked conductor track levels (LB0, LB1) and insulation layers (I); a MEMS substrate (9) with a second front (VS) and a second back (RS); a first micromechanical functional layer (16) formed above the second front surface (VS); a second micromechanical functional layer (17) formed above the first micromechanical functional layer (16), which is connected to the rewiring device (20) via a bond connection (50); wherein a movable sensor structure (MS) is formed in the second micromechanical functional layer (17) which is anchored on one side to the MEMS substrate (9) via a first anchoring area (17b') formed in the second micromechanical functional layer (17); wherein in the second micromechanical functional layer (17) an electrical connection element formed in a second anchoring area (17d; 17d'; 17d'') is anchored on one side via a contact area (52) of the bond connection (50) on the ASIC substrate (10); and wherein the first anchoring area (17b') and the second anchoring area (17d; 17d'; 17d'') are elastically connected to each other via a spring element (17c) formed in the second micromechanical functional layer (17). [2] Micromechanical sensor device according to claim 1, wherein a further electrical contact area is formed in the first anchoring area (17b'). [3] Micromechanical sensor device according to claim 1 or 2, wherein the second anchoring area (17d; 17d'; 17d'') is electrically connected to the rewiring device (20) via the contact area (52). [4] Micromechanical sensor device according to claim 1 or 2, wherein the second anchoring area (17d; 17d'; 17d'') is connected to the rewiring device (20) via an electrically insulating spacer area (I1). [5] Micromechanical sensor device according to one of the preceding claims, wherein the electrical connection element has a perforation (P). [6] Micromechanical sensor device according to claim 4, wherein the electrical contact area (52') together with a conductor track area (LB') formed in the first micromechanical functional layer (16) forms a measuring capacitor structure. [7] Micromechanical sensor device according to claim 3, wherein the electrical contact area (52) together with a conductor track area (LB') formed in the first micromechanical functional layer (16) forms a short-circuit test structure. [8] Micromechanical sensor device according to one of the preceding claims, wherein a cavity (K) is formed between the first front side (VSa) and the second front side (VS) and the first anchoring area (17b') and the second anchoring area (17d; 17d'; 17d'') are each bounded on their unanchored side by the cavity (K). [9] Micromechanical sensor device according to one of the preceding claims, wherein the bond connection (50) has a circumferential bond frame area (51). [10] Micromechanical sensor device according to one of the preceding claims, wherein the spring element (17c) is under preload with respect to the first front face (VSa). [11] Manufacturing process for a micromechanical sensor device comprising the steps: Providing an ASIC substrate (10) with a first front side (VSa) and a second back side (RSa); Forming a rewiring device (20) with a plurality of stacked conductor layers (LB0, LB1) and insulating layers (I) on the front side (VSa) of the ASIC substrate (10); Providing a MEMS substrate (9) with a second front (VS) and a second back (RS); Formation of a first micromechanical functional layer (16) over the front (VS) of the MEMS substrate (9); Formation of a second micromechanical functional layer (17) over the first micromechanical functional layer (16); Forming a movable sensor structure (MS) in the second micromechanical functional layer (17) which is anchored on one side to the MEMS substrate (9) via a first anchoring area (17b') formed in the second micromechanical functional layer (17); Formation of an electrical connection element in a second anchoring area (17d; 17d'; 17d'') in the second micromechanical functional layer (17); Forming a spring element (17c) in the second micromechanical functional layer (17), via which the first anchoring area (17b') and the second anchoring area (17d; 17d'; 17d'') are elastically connected to each other; and Connecting the second micromechanical functional layer (17) to the rewiring device (20) via a bond connection (50), wherein the second anchoring area (17d; 17d'; 17d'') is anchored on one side via a contact area (52) of the bond connection (50) on the ASIC substrate (10). [12] Manufacturing method according to claim 11, wherein a cavity (K) is formed between the first front side (VSa) and the second front side (VS) during joining, such that the first anchoring area (17b') and the second anchoring area (17d; 17d'; 17d'') are each bounded on their unanchored side by the cavity (K).

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