Micromechanical sensor device

Abstract

Micromechanical sensor device (300), comprising: - a MEMS element (100), and - an ASIC element (200), wherein a bonding structure (70) comprising a first bonding layer (50) is formed between the MEMS element (100) and the ASIC element (200), the MEMS element (100) comprising: - a layer arrangement with insulating layers (11, 21) and functional layers (10, 20, 30) arranged alternately on top of one another, wherein a detection element (22) movable in a detection direction (z) is formed in at least one of the functional layers (10, 20, 30); - wherein a spacer element for forming a defined distance between the MEMS element (100) and the ASIC element (200) is formed by means of a further functional layer (40); characterized in that a stop element (40, 50) formed from the spacer element and the first bonding layer (50) is arranged on the detection element (22), wherein an insulating layer (IMD5) is arranged in a stop region of the stop element (40, 50) on the ASIC element (200).

Description

[0001] The invention relates to a micromechanical sensor device. State of the art

[0002] Micromechanical sensors for measuring acceleration and angular rate, for example, are well-known and are mass-produced for various applications in the automotive and consumer sectors. MEMS elements, which are manufactured using surface micromechanical methods, are particularly well-known. In this process, several oxide and polycrystalline silicon layers are deposited and patterned on a silicon substrate. The MEMS wafer is then hermetically sealed with a cap wafer.

[0003] Fig. Figure 1 shows a cross-sectional view of a conventional surface micromechanical sensor. In this example, a MEMS wafer 100 comprises three functional layers in the form of polysilicon layers 10, 20, 30, which can be patterned largely independently of one another. The oxide layers 11, 21 located between them can be opened at specific locations to create vias between the polysilicon layers 10, 20, 30. The first polysilicon layer 10 preferably functions as an electrical wiring layer, while the second polysilicon layer 20 and the third polysilicon layer 30 can be used both for wiring and for implementing movable MEMS structures. The MEMS structures are exposed, for example, by targeted removal of the oxide layers 11, 21 beneath the polysilicon layers 10, 20, 30 by etching with gaseous HF.

[0004] The MEMS element, for example an acceleration or yaw rate sensor, has at least one mechanical suspension 33, at least one spring arrangement 31 and movable mass and electrode elements 22, 32, which in the example of Fig. 1 are realized in both the second polysilicon layer 20 and the third polysilicon layer 30. A portion of the movable mass 22 realized in the second polysilicon layer 20 forms a capacitor arrangement across the gaps 13 and 23 with the lower fixed electrode 12 located in the first polysilicon layer 10 and the upper fixed electrode 32 realized in the third polysilicon layer 30.

[0005] Specific design topologies for such arrangements are known, for example, from DE 10 2009 000 167 A1 for a z-acceleration sensor and from DE 10 2009 000 345 A1 for a yaw rate sensor with detection deflections in the z-direction. As an alternative to functioning as an upper electrode, the element of the third polysilicon layer 30 can also define a mechanical stop, which is preferably set to the same electrical potential as the movable MEMS structure.

[0006] A problem with such MEMS structures can be the mechanical robustness of the mass or electrode element implemented in the second polysilicon layer 20 when the structure is deflected upward and strikes the overlying element of the third polysilicon layer 32. Particularly when the plane of the second polysilicon layer 20 is relatively thin, for example, with a thickness of approximately 1 µm to approximately 3 µm, the risk of mechanical fracture of the MEMS structure upon exposure to high overload (“drop test”) is quite high. The z-stop 81 implemented in the cap wafer 80 is ineffective if the gap 23 between the second polysilicon layer 20 and the third polysilicon layer 30 is smaller than the gap 61 between the top side of the third polysilicon layer 30 and the bottom side of the cap stop 81.

[0007] To prevent fractures in the structure of the second polysilicon layer 20, spring-loaded structures of the third polysilicon layer 30 were proposed, for example, in DE 10 2011 080 982 A1, which can absorb mechanical energy upon impact and thereby limit the mechanical stresses of the second polysilicon layer 20. However, the design of these structures is complex and requires additional space.

[0008] For example, methods of vertical integration, or hybrid integration or 3D integration are known from US 7250353B2, US 7442570 B2, US 2010 0109102 A1, US 2011 0049652 A1, US 2011 012247 A1, US 2012 0049299 A1, and DE 10 2007 048604 A1, in which at least one MEMS wafer and one evaluation ASIC wafer are mechanically and electrically connected to one another via wafer bonding processes.

[0009] Such vertical integration processes are particularly useful in combination with through-silicon vias (TSV) and flip-chip technologies, whereby construction and contacting can be carried out as a chip-scale package, as is known, for example, from US 2012 0049299 A1 and US 2012 0235251 A1.

[0010] The subsequently published patent application DE 10 2014 211 333 A1 discloses a micromechanical component.

[0011] The published patent application DE 10 2012 219 465 A1 discloses a method for producing a cap for a MEMS component.

[0012] The subsequently published patent application DE 10 2013 217 726 A1 discloses a micromechanical component for a capacitive sensor device. Disclosure of the invention

[0013] It is an object of the present invention to improve the mechanical robustness of a micromechanical sensor device, in particular a vertically integrated micromechanical sensor device.

[0014] The object is achieved according to a first aspect with a micromechanical sensor device having the features of claim 1, comprising: - a MEMS element, and - an ASIC element, wherein a bond structure is formed between the MEMS element and the ASIC element, the MEMS element comprising: - a layer arrangement with insulating layers and functional layers arranged alternately on top of one another, wherein a detection element movable in a detection direction is formed in at least one of the functional layers; - wherein a spacer element for forming a defined distance between the MEMS element and the ASIC element is formed by means of a further functional layer;characterized in that a stop element with the spacer element and a first bonding layer is arranged on the detection element, wherein an insulating layer is arranged in a stop region of the stop element on the ASIC element.

[0015] In this way, an existing layer arrangement is used to form a stop element and is arranged on the movable detection element. This advantageously provides effective upward stop protection at low additional cost, providing a defined stop behavior in the z-direction. Thus, in the event of a stop, the stop first occurs on the ASIC wafer in a defined manner. Advantageously, this requires only minor adjustments to the layout and no changes to the overall process.

[0016] According to a further aspect, which is not part of the invention, the object is achieved with a method for producing a micromechanical sensor device, comprising the steps: - Providing a MEMS element; - Providing an ASIC element; - forming a sensing element in the MEMS element, wherein a stop element is arranged on the sensing element, wherein an insulating layer is formed in a stop region for the stop element on the ASIC element; and - Forming a bond structure between the MEMS element and the ASIC element.

[0017] Preferred embodiments of the sensor device are the subject of subclaims.

[0018] A preferred embodiment of the sensor device provides that the detection element has a section formed orthogonally to the detection direction. This configuration of the sensor device advantageously prevents the orthogonal section from potentially breaking in the event of an impact.

[0019] A further embodiment of the micromechanical sensor device is characterized in that it has at least one electrode that interacts with the sensing element. This supports the smooth functional interaction of the sensing element with the electrode.

[0020] Another embodiment of the sensor device is characterized in that the distance between the stop element and the ASIC element is greater than the detection gap to the electrode. Despite any upward impact, no impact occurs between the stop element and the electrode.

[0021] Another embodiment of the sensor device is characterized in that the spacer element comprises a polysilicon layer. This advantageously allows a layer already present in the manufacturing process to be used to form the spacer element. The stop element is preferably dimensioned such that a certain defined minimum distance is maintained between the MEMS and ASIC wafers.

[0022] Another embodiment of the sensor device is characterized in that the first bonding layer of the spacer element is one of the following: germanium, aluminum, or metal. In this way, a metallic bonding structure for bonding the MEMS wafer to the ASIC wafer can be realized.

[0023] A further embodiment of the sensor device is characterized in that an oxide material is arranged opposite the stop element on the ASIC in the stop direction. This advantageously prevents an electrical short circuit from occurring when the movable element strikes the ASIC. This advantageously prevents damage within the sensor device.

[0024] A further embodiment of the sensor device is characterized in that the detection element is formed in a single functional layer.

[0025] In this way, the design diversity for the sensor device is advantageously increased.

[0026] The invention, along with further features and advantages, is described in detail below with reference to several figures. All described features constitute the subject matter of the invention, regardless of their representation in the description or figures, and regardless of their reference in the claims. Identical or functionally equivalent elements have the same reference numerals.

[0027] In the figures shows: Fig. 1 a cross-sectional view through a conventional micromechanical sensor device; Fig. 2 a cross-sectional view through a conventional vertically integrated sensor device Fig. 3 a partial view of the sensor device of Fig. 2; Fig. 4 a cross-sectional view of an embodiment of a sensor device according to the invention; Fig. 5 a cross-sectional view through the sensor device of Fig. 4 in case of an attack; Fig. 6 and Fig. 7 further embodiments of the sensor device according to the invention; and Fig. 8 is a basic flow diagram of an embodiment of a method which is not part of the invention; and Description of embodiments

[0028] In the following, the term “defined base distance” refers to a distance between the MEMS element and the ASIC element that ensures that there is no crosstalk from one wafer to the other.

[0029] Fig. Figure 2 shows a known vertical integration concept for a micromechanical component, which comprises a MEMS element 100 consisting of a MEMS silicon substrate, at least one wiring level, at least one MEMS functional layer, and a plurality of oxide layers grown or deposited thereon. The functional layers can also be applied using wafer bonding processes and subsequent grinding back. The ASIC element 200, which is preferably manufactured using a CMOS process, consists of a silicon substrate, doped semiconductor layers for implementing the electrical circuits, and the metal oxide stack, in particular for wiring and for implementing capacitors.

[0030] The MEMS element 100 and the ASIC element 200 are connected to each other using a metallic wafer bonding process, e.g., via eutectic bonding of aluminum with germanium. For example, the topmost aluminum wiring layer on the ASIC element 200 is used as the bonding surface, and germanium is deposited on the MEMS element 100 as the top layer. The two wafers 100, 200 are then pressed together at temperatures above approximately 430°C with sufficient pressure to create a eutectic liquid phase. The aluminum-germanium bond hermetically encapsulates the MEMS structures using a surrounding bonding frame and also enables electrical contacts between the MEMS element 100 and the ASIC element 200. Other metallic bonding processes, such as copper-tin bonding or thermocompressive processes, are also conceivable.The electrical communication of the ASIC 200 from and to the outside preferably takes place via metallic through-silicon vias (TSVs), which are opened on the back of the ASIC 200 and then routed via a rewiring level above an insulation layer and solder ball 400 to an application circuit board (not shown), for example in a mobile phone.

[0031] The ASIC element 200 has several wiring and insulation layers. Fig. For the sake of simplicity and clarity, Figure 3 shows only a part of the layers involved, in particular the MEMS element 100 starting from the first polysilicon layer 10. Furthermore, in all subsequent figures, the wafer stack is reversed so that the MEMS element 100 is at the bottom and the ASIC element 200 is at the top. The section of Fig. 3 essentially corresponds to the Fig. 2 dashed area B.

[0032] In contrast to the MEMS element 100 from Fig. 1, the MEMS element 100 of Fig. 3, a further silicon layer in the form of a fourth polysilicon layer 40, which is arranged on the third polysilicon layer 30 and acts as a spacer between the MEMS and ASIC wafers. Furthermore, a first bonding layer, e.g., in the form of a germanium layer 50, is arranged on the fourth polysilicon layer 40 in the region to be eutectic bonded. This first bonding layer is opposite corresponding (i.e., similar in terms of topology and areas) structures in an uppermost metal level M6 of the ASIC element 200.

[0033] After wafer bonding, a eutectic aluminum-germanium bond 70 is created in the area of the bond frame. However, the problem described above for the mechanical robustness of the MEMS element 100 disadvantageously remains almost unchanged after bonding has been carried out, since a gap 23 between the second polysilicon layer 20 and the third polysilicon layer 30 is smaller than a gap between the third polysilicon layer 30 and the M6 level of the ASIC element 200. Accordingly, a disadvantageous impact of the MEMS element 200 between the second and third polysilicon layers 20, 30 can also occur here.

[0034] According to the invention, it is therefore provided for a local use of the fourth polysilicon layer 40 and the first bonding layer 50 on the MEMS wafer 100 in order to realize defined mechanical z-stops on the movable sensing element 22. In the area of the stops, the top metal layer M6 is removed on the ASIC side. This results in small residual gaps between the MEMS element 100 and the ASIC element 200, which are smaller than the gaps between the functional polysilicon levels in the MEMS element 100 (first to third polysilicon layers 10, 20, 30).

[0035] Advantageously, in the event of a collision, due to the small residual gap between the MEMS element 100 and the ASIC element 200, the movable MEMS structure can strike the ASIC element 200 and no longer the polysilicon layers, which are highly susceptible to breakage. This advantageously increases the mechanical robustness of the entire MEMS structure.

[0036] Since the stop is made in a defined manner on an IMD5 insulation layer, electrical short circuits can also be avoided. This advantageously eliminates the potentially very complex wiring of z-stops in the MEMS element 100, which must have the same electrical potential as the moving mass to prevent short circuits.

[0037] Fig. Figure 4 shows this arrangement according to the invention, in which a z-stop is arranged on the fourth polysilicon layer 40 and on the first bonding layer 50 on a partial area of the movable third polysilicon layer 30. The resulting residual gap 61 between the germanium layer 50 and the insulation layer IMD5 on the side of the ASIC element 200 is now smaller than the gap 23 between the second and third polysilicon layers 20, 30. For large vertical deflections, the first mechanical stop therefore occurs at the stop structure 40, 50 and no longer between the polysilicon layers 20, 30, as shown in Fig. 5 is indicated in principle. It can be seen that the section 22a of the detection element 22, which is formed orthogonally in the z-stop direction, has a distance from the electrode 32, although the stop event has already occurred.

[0038] Another embodiment of the sensor device is characterized in that the non-conductive material IMD5 in the impact area of the ASIC element 200 is an oxide material. Due to the fact that the MEMS structure is at a defined potential when it strikes upwards, a short circuit does not occur. However, if the sensor were to strike metal, the metal's potential would have to be the same as the MEMS structure's potential to reliably prevent damage.

[0039] Advantageously, the invention is not limited to MEMS elements 100 with partially overlapping regions of the second and third polysilicon layers 20, 30, but can also be used beneficially for other arrangements.

[0040] Fig. 6 shows a MEMS element 100, which is also formed from elements of the second and third polysilicon layers 20, 30, but does not have a counter electrode or z-stop in the third polysilicon layer 30. However, it does have a counter electrode in the uppermost metal level M6 of the ASIC element 200. In this case, the inventive arrangement of the stop with the arrangement of the fourth polysilicon layer 40 and the germanium layer 50 is advantageous for preventing an electrical short circuit between the movable MEMS structure and the ASIC counter electrode in the event of high mechanical overload.

[0041] Fig. 7 shows a similar arrangement as Fig. 6 with the only difference that the movable MEMS element 100 is only implemented in the third polysilicon layer 30. The advantages are the same as above in connection with Fig. 6 were described.

[0042] Fig.8 shows a basic sequence of an embodiment of a method for producing a micromechanical sensor device 300, wherein the method is not part of the invention.

[0043] In a first step S1, a MEMS element 100 is provided.

[0044] In a second step S2, an ASIC element 200 is provided.

[0045] In a third step S3, a detection element 22 is formed in the MEMS element 100, wherein a stop element 40, 50 is arranged on the detection element 22, wherein an insulating layer IMD5 is formed in a stop region for the stop element 40, 50 on the ASIC element 200.

[0046] Finally, in a fourth step S4, a bond structure 70 is formed between the MEMS element 100 and the ASIC element 200.

[0047] In summary, the present invention proposes a micromechanical sensor device that advantageously provides a defined stop for the sensor device. This is particularly advantageous in the case of greatly increased acceleration forces that can occur when electronic devices impact the ground. This advantageously prevents damage to the sensitive MEMS structures. These forces can also occur due to strong vibrations during chip singulation and can be mitigated according to the invention.

[0048] Although the invention has been described above using specific embodiments, it is by no means limited thereto. Those skilled in the art will thus be able to appropriately modify or combine the described features without deviating from the essence of the invention.

Claims

[1] Micromechanical sensor device (300), comprising: - a MEMS element (100), and - an ASIC element (200), wherein a bonding structure (70) comprising a first bonding layer (50) is formed between the MEMS element (100) and the ASIC element (200), the MEMS element (100) comprising: - a layer arrangement with insulating layers (11, 21) and functional layers (10, 20, 30) arranged alternately on top of one another, wherein a detection element (22) movable in a detection direction (z) is formed in at least one of the functional layers (10, 20, 30); - wherein a spacer element for forming a defined distance between the MEMS element (100) and the ASIC element (200) is formed by means of a further functional layer (40); characterized bythat a stop element (40, 50) formed from the spacer element and the first bonding layer (50) is arranged on the detection element (22), wherein an insulating layer (IMD5) is arranged in a stop region of the stop element (40, 50) on the ASIC element (200). [2] Micromechanical sensor device (300) according to claim 1, characterized by that the detection element (22) has a section (22a) formed orthogonally to the detection direction (z). [3] Micromechanical sensor device (300) according to claim 1 or 2, characterized by that it has at least one electrode (12, 32) cooperating with the detection element. [4] Micromechanical sensor device (300) according to claim 3, characterized by that a distance of the stop element (40, 50) to the ASIC element (200) is greater than a detection gap (23) to the electrode (32). [5] Micromechanical sensor device (300) according to one of the preceding claims, characterized by that the spacer element (40, 50) has a polysilicon layer. [6] Micromechanical sensor device (300) according to one of the preceding claims, characterized by that the first bonding layer (50) of the spacer element (40, 50) is one of the following: germanium, aluminum, metal. [7] Micromechanical sensor device (300) according to one of the preceding claims, characterized by that an oxide material is arranged on the ASIC (200) opposite the stop element (40, 50) in the stop direction (z). [8] Micromechanical sensor device (300) according to one of the preceding claims, characterized by that the detection element (22) is formed in a single functional layer (10, 20, 30).

Images