BOND STRUCTURES ON MEMS ELEMENT AND ASIC ELEMENT

Abstract

A MEMS element is provided. The MEMS element includes: a substrate; a first passivation layer arranged on the substrate; a metal layer arranged on the first passivation layer; a second passivation layer arranged on the metal layer and on the first passivation layer; and a punch element, an electrically conductive diffusion-blocking layer being arranged on the punch element and on the second passivation layer, a first bonding element being arranged on the punch element.

Claims

1-14. (canceled)

15. A MEMS element, comprising: a substrate; a first passivation layer arranged on the substrate; a metal layer arranged on the first passivation layer; a second passivation layer arranged on the metal layer and on the first passivation layer; and a punch element, an electrically conductive diffusion-blocking layer being arranged on the punch element and on the second passivation layer, a first bonding element being arranged on the punch element.

16. The MEMS element as recited in claim 15, wherein a material of the punch element is aluminum or a dielectric material.

17. The MEMS element as recited in claim 15, wherein the diffusion-blocking layer is diffusionally stable relative to the first bonding element.

18. The MEMS element as recited in claim 15, wherein the diffusion-blocking layer includes notches in a planar area.

19. The MEMS element as recited in claim 15, wherein the diffusion-blocking layer includes two partial blocking layers.

20. The MEMS element as recited in claim 19, wherein a first one of the two partial blocking layer is structured.

21. The MEMS element as recited in claim 16, wherein the punch element is arranged on the first passivation layer.

22. The MEMS element as recited in claim 15, wherein the punch element is arranged on an opening of the second passivation layer.

23. The MEMS element as recited in claim 15, wherein the punch element is arranged on the first passivation layer, mutually delimited openings of the first passivation layer being arranged around the punch element, the diffusion-blocking layer being arranged on the second passivation layer and on the openings of the first passivation layer.

24. The MEMS element as recited in claim 15, wherein the material of the punch element is a dielectric material, and the diffusion-blocking layer is structured.

25. An ASIC element, comprising: a second substrate; an ASIC functional layer arranged on the second substrate; a metal layer arranged on the ASIC functional layer and an oxide layer having vias; and a passivation layer arranged on the oxide layer, the passivation layer being formed as a spacer element and a trough element, a bonding element being able to be plunged into the trough element during a eutectic bonding process, an outflowing of eutectic material being preventable.

26. The ASIC element as recited in claim 25, wherein a metal structure is formed in the passivation layer, the metal structure being separated from the second bonding element.

27. A micromechanical sensor, comprising: a MEMS element, including: a substrate; a first passivation layer arranged on the substrate; a metal layer arranged on the first passivation layer; a second passivation layer arranged on the metal layer and on the first passivation layer; and a punch element, an electrically conductive diffusion-blocking layer being arranged on the punch element and on the second passivation layer, a first bonding element being arranged on the punch element; and an ASIC element, including: a second substrate; an ASIC functional layer arranged on the second substrate; a metal layer arranged on the ASIC functional layer and an oxide layer having vias; and a passivation layer arranged on the oxide layer, the passivation layer being formed as a spacer element and a trough element, the first bonding element being able to be plunged into the trough element during a eutectic bonding process, an outflowing of eutectic material being preventable; wherein the ASIC element is eutectically bonded to the MEMS element.

28. A method for manufacturing a micromechanical sensor, comprising the following steps: providing a sensor element; providing a MEMS element having a dimensionally stable punch element and a first bonding element arranged on the punch element; providing an ASIC element having a trough structure formed in a passivation layer having a second bonding element arranged in the trough structure, and a spacer structure; and eutectic bonding the MEMS element to the ASIC element in such a way that the punch element plunges into the trough structure and such that a defined separation is established between the MEMS element and the ASIC element by way of the spacer structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG. 1 shows a cross-sectional view of specific embodiments of an example MEMS element and the ASIC element prior to a bonding process in accordance with the present invention.

[0041] FIG. 2 shows a cross-sectional view of a specific embodiment of the example chip-to-chip contact after a bonding process in accordance with the present invention.

[0042] FIG. 3 shows a cross-sectional view of specific embodiments of the example MEMS element and the ASIC element prior to a bonding process in accordance with the present invention.

[0043] FIG. 4 shows a cross-sectional view of further specific embodiments of the example MEMS element and the ASIC element prior to a bonding process in accordance with the present invention.

[0044] FIG. 5 shows a cross-sectional view of further specific embodiments of the example MEMS element and the ASIC element prior to a bonding process in accordance with the present invention.

[0045] FIG. 6 shows a cross-sectional view of further specific embodiments of the example MEMS element and the ASIC element prior to a bonding process in accordance with the present invention.

[0046] FIG. 7 shows a top view of a specific embodiment of the example chip-to-chip contact in accordance with the present invention.

[0047] FIG. 8 shows a top view of a further specific embodiment of the example chip-to-chip contact in accordance with the present invention.

[0048] FIG. 9 shows a cross-sectional view of a further specific embodiment of a MEMS element prior to a bonding process in accordance with the present invention.

[0049] FIG. 10 shows a basic sequence of a method for manufacturing an example micromechanical sensor in accordance with the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0050] A main feature of the present invention is to provide improved chip-to-chip contact. The example chip-to-chip contact in accordance with the present invention can be used in general to connect two components by eutectic bonding and is advantageously not limited to a use in a pressure sensor, but can be used for a variety of micromechanical sensor types (such as inertial sensors).

[0051] The example chip-to-chip contact functions as a way to provide a reliable electrical connection between the components to be connected, i.e., between the last metal layers in a MEMS element and in an ASIC element.

[0052] Such eutectic bonding is accomplished through the alloying of germanium (on the MEMS element) and aluminum (the last metal layer of the ASIC element). However, it is advantageous that the present invention is not limited to this specific eutectic bond connection but can be implemented using other conventional bonding partners. Examples of suitable metallic bonding methods include AlGe, AuSi, CuSn, AlAl, CuCu, AuAu, etc.

[0053] During the bonding process, which is carried out at high temperature, all of the available aluminum and germanium melts and for a sufficiently short period of time exists primarily as a liquid with isolated solid grains in it.

[0054] At temperatures in the vicinity of or above the eutectic temperature, aluminum is very soft and can be easily compressed using contact pressure. Full eutectic melting of aluminum is not required here. Even small additional amounts of germanium in aluminum lead to further significant softening of the aluminum. There is no significant volume change due to the alloying of aluminum and germanium, which means that as a first approximation it can be assumed that the process is volume neutral.

[0055] FIG. 1 shows a cross section of chip-to-chip contact elements prior to bonding, and FIG. 2 shows a cross section of said elements after bonding.

[0056] Seen in FIG. 1 is a MEMS element 100 having a substrate in the form of a silicon layer 10, a first passivation layer 20 being arranged on the silicon layer (for example in the form of an oxide layer SiO.sub.2). A second passivation layer 40 and a first metal layer 30 are arranged on first passivation layer 20. Here, as shown in FIG. 1, at least a part of second passivation layer 40 may be arranged next to metal layer 30 on first passivation layer 20. Furthermore, second passivation layer 40 covers metal layer 30 at least partially. Second passivation layer 40 has an opening 41, a punch element 60 being arranged on the opening 41 of second passivation layer 40. This opening 41 can directly represent a connection of punch element 60 to metal layer 30, for example in that opening 41 is formed above metal layer 30 (from the perspective of the substrate) or directly lateral to metal layer 30. Punch element 60 can be made of aluminum or a dielectric material, for example silicon dioxide or silicon nitride. An electrically conducting diffusion-blocking layer 50 is arranged on punch element 60. A first bonding element 70 (for example germanium) is arranged on diffusion-blocking layer 50 at punch element 60.

[0057] In the lower section of FIG. 1, a cross section of an ASIC element 200 is shown, comprising a silicon layer 110 on which an

[0058] ASIC functional layer 120 is arranged, the functional layer comprising a plurality of metal layers, vias and oxide layers (not shown) for creating the ASIC functionality (ASIC back end) of ASIC element 200. A second metal layer 121 is arranged on ASIC functional layer 120, as is a further oxide layer 130 in which electrical vias 122 are formed. A passivation layer 140 is formed on oxide layer 130 as a spacer structure which forms a trough-like structure, a second bonding element 123 (for example aluminum) being arranged in the passivation layer.

[0059] This results in the following areas inside a feasible chip-to-chip contact, the areas having the following functions:

[0060] Punch element 60 provides a mechanical connection after bonding, punch element 60 not deforming during and after the bonding. Punch element 60 thus represents a reference parameter for the mechanical connection between MEMS element 100 and ASIC element 200. Punch element 60 pushes the Ge structure sufficiently far into the opposing passivation opening such that when the two wafers are pressed together the germanium comes first into contact with the opposing aluminum. In addition, punch element 60 must establish the electrical contact between the eutectic material and the sensor conductor path.

[0061] The trough structure of passivation layer 140 defines the area in which the liquid eutectic material 141 (for example aluminum-germanium) is located. It must reliably compensate for process tolerances, layer thickness and structure widths so that no alloyed aluminum-germanium is forced out of the trough and so that punch element 60 reliably comes to lie inside the trough (taking into account the bond shift due to adjustments).

[0062] The spacer structure on passivation layer 140 seals the chip-to-chip contact, defines the height of the trough and absorbs the force in effect due to the pressing force during the bonding process once the eutectic material 141 has melted.

[0063] FIG. 2 shows a cross section through a chip-to-chip contact after bonding of MEMS element 100 to ASIC element 200.

[0064] Thus, the dimensioning of the eutectic material 141 and the individual areas results from the following:

[0065] - punch element 60, whose surface area linearly scales the mechanical load capacity and the electrical conductivity. In the process, the height of punch element 60 is preferably selected such that it is greater than a passivation thickness of ASIC element 200. In addition, punch element 60 should advantageously come to lie below the initial Al surface after bonding, supporting a more reliable, stable bond. In order to accomplish this reliably, the height, the process tolerances, and the layer thicknesses which define the punch height should be taken into account, as should the layer thickness of passivation layer 140. It is preferable for the rectangular punch element 60 to have edge lengths in the range of between approximately 10 m and approximately 100 m in order to achieve plunging below the initial aluminum surface to an extent of approximately 0 to approximately 1 m. [0066] a trough structure, which after bonding is vertically defined by a passivation of MEMS element 100 and of punch element 60 on the MEMS side, and on the ASIC side is defined by the adjacent last metal plane. In the horizontal respect, the trough is defined by the spacer structure of passivation layer 140. A width of the trough is defined by the width of punch element 60 plus the bond shift on the left and the right.

[0067] A height of the trough structure is defined by the total of the layer thicknesses of the metal layer of second bond element 123 and passivation layer 140. The compensating volume of the trough structure is particularly important, being primarily defined by the spacing of punch element 60 and the height of passivation layer 140 and its distance to punch element 60. The AlGe interface comes to lie in this volume (compensating volume) after the bonding process. This volume is defined by the process tolerances of punch element 60 and of passivation layer 140 and that of bond elements 70, 123. The volume is further defined by the displaced volume due to the plunging below the initial aluminum surface. [0068] a spacer structure of passivation layer 140 which prevents outflow of eutectic material 141 from the trough structure. In an optimized specific embodiment, a distance of 1 m to 10 m is provided between the trough and the spacer structure. This distance also ensures against breakage of the trough edge so that no germanium can make its way to the aluminum substructure of the spacer. [0069] a eutectic material 141 whose volume ratio between the bond elements (e.g. Ge and Al) should be selected to be as close to the eutectic ratio as possible. A germanium deviation in the direction of too much should be avoided here. Also, the volume ratio should be selected such that at nominal layer thicknesses the compensation volume of the trough structure is at most approximately half-filled. The germanium volume should be as wide (approximately 10 m to approximately 100 m) and as thin (approximately 100 nm to approximately 1 m) as possible. The germanium structure should be within the width of punch element 60. In the Al volume, the width is defined by the trough width. The height of the Al volume should be in the order of magnitude of approximately 0.5 m to approximately 2 m. The Al layer may advantageously have a small interruption of approximately 1 m next to punch element 60 on the left and right, a eutectic ratio thereby being easier to achieve below punch element 60.

[0070] The cross section shown in FIGS. 1 and 2 is an example of a cross section of an example chip-to-chip contact for a pressure sensor (not shown). The layers and their functions are as follows:

[0071] The electrical first passivation layer 20 between the metal conductor path and the silicon may be made of SiO.sub.2. The layer thickness is in the order of magnitude of 0.1 m to 1 m.

[0072] Metal layer 30 forms an electric conductor path of MEMS element 100. It can be made of aluminum, with its layer thickness being in the order of magnitude of 0.1 m to 1 m.

[0073] The electrical second passivation layer 40 on the metal conductor path may be made of SiN (silicon nitride), with its layer thickness being approximately 0.1 m to approximately 1 m.

[0074] Punch element 60 may be made of a dielectric material (such as SiO2 or SiN) depending on the specific embodiment or may be electrically conducting (for example aluminum).

[0075] Diffusion-blocking layer 50 is electrically conducting and must be diffusionally stable relative to the metal layers 30, 123 and relative to eutectic material 141. It may be made of Ti, TiN, Ta, TaN, and combinations of said elements and compounds, among other things. The overall layer thickness of diffusion-blocking layer 50 is in the order of magnitude of approximately 0.05 m-approximately 2 m.

[0076] Passivation layer 140 is made of a dielectric material, which can be made of SiO.sub.2 or silicon nitride or a combination of the two compounds. The layer thickness is in the order of magnitude of approximately 0.2 m to approximately 2 m.

[0077] The metal layer of second bond element 123 represents the last metal layer of ASIC element 200 and is preferably made of aluminum. The layer thickness of this metal layer is in the order of magnitude of approximately 0.5 m to approximately 2 m.

[0078] Further embodiment variations of the example chip-to-chip contact are shown in further figures in cross section. The goal in each case is to pass the electrical connection of electric metal layer 30 of MEMS element 100 through the eutectic material to the metal layer (the last metal layer) of ASIC element 200 and finally into ASIC functional layer 120 through the via between the last and the next-to-last metal layer 121.

[0079] The cross-sectional view of FIG. 3 corresponds to that of FIG. 2. The cross section of punch element 60 is made up of the following layer sequence: electrical passivation layer 20, first metal layer 30, second passivation layer 40, punch element 60 and diffusion-blocking layer 50. The material of punch element 60 may be made of an electrically conductive material such as aluminum. Thus, opening 41 may lie in second passivation layer 40 below punch element 60. Diffusion of germanium into punch element 60 must be prevented, therefore a closed and stable diffusion-blocking layer 50 is provided in the case where punch element 60 is made of aluminum.

[0080] The stability of the covering diffusion-blocking layer 50 can sometimes present problems. For this reason, diffusion-blocking layer 50 may alternatively be split up into two partial diffusion-blocking layers 50a, 50b as shown in FIG. 4. In the process, a first blocking layer 50a lies below punch element 60 and a second blocking layer 50b lies above punch element 60. Thus, penetration of germanium into punch element 60 is possible, but further diffusion of germanium into metal layer 30 is prevented by first blocking layer 50a in the opening of passivation layer 40 on metal layer 30.

[0081] Even if a small amount of germanium penetrates into the aluminum of punch element 60, the punch element will become very soft and will tend to be squished excessively. Furthermore, a collapsing/cracking of second partial diffusion-blocking layer 50b may cause a comparatively large amount of aluminum to take part in the eutectic bond. Thus, because of the probability distribution of breakage, it becomes difficult to keep the aluminum-to-germanium ratio near the eutectic ratio. Therefore, in a variant not shown in the figures, the first partial diffusion-blocking layer 50a may lie directly on metal layer 30 or on part of metal layer 30.

[0082] Alternatively, the punch material of punch element 60 may, as indicated in FIG. 5 in color, also be a dielectric material, such as SiO2 or SiN. No germanium penetrates into these layers, they are sufficiently stable and thick so that penetration of germanium into metal layer 30 is no longer possible as per the layout. Also advantageous is the fact that diffusion-blocking layer 50 may be structured since deposition of germanium directly on the punch material is also possible. This structuring of diffusion-blocking layer 50 facilitates a better mechanical connection of the eutectic material 141 to punch element 60 since eutectic material 141 wetting on diffusion-blocking layer 50 is worse than it is on the punch element made of SiO.sub.2 or SiN. In this case, the electrical resistance, defined by the diffusion-blocking layer 50, runs along the contour of punch element 60. Since the conductivity and protective layer thickness of diffusion-blocking layer 50 is significantly less than punch element 60 in aluminum, the parasitic resistance is therefore higher in comparison to the specific embodiments of FIGS. 3 and 4.

[0083] In order to reduce the electrical resistance of the specific embodiment of FIG. 5, opening 41 in second passivation layer 40 may be formed next to and around punch element 60. This eliminates the need to split up diffusion-blocking layer 50 into two partial diffusion-blocking layers 50a, 50b as explained in FIGS. 4 and 5.

[0084] Possible variants of the chip-to-chip contact are shown in

[0085] FIGS. 7 and 8 in top views. The rectangular shape makes it possible to design the chip-to-chip contact at as small a scale as possible. In particular, the size of the chip-to-chip contact here is a function of the size of punch element 60, which may be between approximately 5 m and approximately 100 m. In addition, in the design of the chip-to-chip contact, care must be taken that electrically conductive diffusion-blocking layer 50 is not structured past any topographical edge, but rather is structured in the plane only.

[0086] The reason for this is that whereas the deposition of diffusion-blocking layer 50 occurs relatively conformally, the structuring of diffusion-blocking layer 50 is very directional relative to the normal of the wafer surface. For directional etching, the conformal diffusion-blocking layer 50 appears to have a greater layer thickness than it does on planar areas. The result is that in planar areas diffusion-blocking layer 50 is completely removed, but at topographical edges residue remains behind. Excess etching to remove this residue is not allowed since this has a negative effect on the sensor's performance.

[0087] Structuring within diffusion-blocking layer 50 is necessary so as to electrically separate the chip-to-chip contacts from one another, electrical conductor paths of metal layer 30 being routed out from the chip-to-chip contact in this way.

[0088] A possible specific embodiment for this structuring of diffusion-blocking layer 50 is shown in FIG. 7, which represents a larger specific embodiment. Here, diffusion-blocking layer 50 is structured on the closed metal layer 30. The inner edge of notch 50c of diffusion-blocking layer 50 has the dimension of the spacer of passivation layer 140 plus the peripheral edge of the bond shift due to adjustment. The width of notch 50c of diffusion-blocking layer 50 defines the electrical insulation relative to ground potential, said width preferably being between approximately 1 m and approximately 30 m. The distance of metal layer 30 to the edge of diffusion-blocking layer 50 is defined by the lithography adjustment shift, the result being a length of metal layer 30 which ultimately defines a maximum dimension A of the chip-to-chip contact. Furthermore, there is an electrical feed 30a to a sensor element which is not shown.

[0089] FIG. 8 shows the smaller specific embodiment of the chip-to-chip contact. Here, the fact is utilized that for a pressure sensor, electrical connections are present in substrate 10. Therefore, the electrical connection from the chip-to-chip contact to the conductor paths of metal layer 30 is cut through substrate 10 in the form of a Si passage 11 with Si vias 11a. A parasitic resistance of this Si passage 11 remains within a reasonable range. In order to further shrink the chip-to-chip contact, spacers of passivation layer 140 for spacing MEMS element 100 are left out. These are not necessary for the chip-to-chip contact since they are integrated into the bond frame which has a larger surface area. In this way, the eutectic material 141 of the chip-to-chip contact remains open in the variant of FIG. 8.

[0090] In conventional bond frames and chip-to-chip contacts, metal surface 30 have a planar design. These comparatively large aluminum surfaces soften at temperatures near the eutectic bond temperature, which reduces the mechanical stability of the MEMS back end, which is made up of passivation layer 20, metal layer 30, passivation layer 40, punch element 60 and blocking layer 50. This causes the mechanical load on passivation layer 40, which surrounds metal layer 30, to increase, and thus the risk for cracks in passivation layer 40. This can be counteracted using a mesh-like structuring of metal layer 30 with small line widths which are small enough that they are filled up by the deposition of passivation layer 40 and are thus topography-free.

[0091] Alternatively, an alternative punch design can be provided for this purpose as shown in FIG. 9. In this alternative, metal layer 30 in punch element 60 is removed and the layer thickness of punch element 60 is increased accordingly, this only being possible when punch element 60 is made of a dielectric material.

[0092] Since punch element 60 is also part of the bond frame, it must consequently be implemented identically there. In addition, the electrical connection in metal layer 30 must be ensured for there to be chip-to-chip contact. This can be done in accordance with the specific embodiment shown in FIG. 6.

[0093] In a further alternative specific embodiment, the bond frame can represent an electrical chip-to-chip contact. For this purpose, a smaller bond frame area may be provided having the cross section of a chip-to-chip contact, which is preferably a contact to ground potential.

[0094] FIG. 10 shows a basic method for manufacturing a micromechanical sensor.

[0095] In a step 400, a sensor element is provided.

[0096] In step 410, a MEMS element 100 is provided having a dimensionally stable punch element 60 and a first bond element 70 arranged thereon.

[0097] Provided in a step 420 are an ASIC element 200 having a trough structure formed in a passivation layer 140, a second bond element 123 and a spacer structure being arranged in said trough structure.

[0098] In a step 430, a eutectic bonding of MEMS element 100 to ASIC element 200 is carried out in such a way that punch element 60 plunges into the trough structure and a defined separation between MEMS element 100 and ASIC element 200 is established by way of the spacer structure.

[0099] Although the present invention has been described above using concrete application examples, a person skilled in the art, without straying from the essence of the present invention, can also implement specific embodiments which are not, or are only partially, disclosed.