MEMS PACKAGE AND METHOD FOR ENCAPSING A MEMS STRUCTURE

Description

[0001] The present invention relates to a method for encapsulating a MEMS structure, such as one with a movable element, for example in quasi-static MEMS components such as MEMS vector scanners. The present invention further relates to a MEMS package. The present invention further relates to arranging a wafer stack for hermetic encapsulation with a defined internal pressure for a quasi-static MEMS component.

[0002] MEMS vector scanners are encapsulated using a hybrid assembly, such as a ceramic package.

[0003] MEMS vector scanners have complex structures for high mechanical efficiency, such as a 3D design where the actuators and the mirror plate are located on different planes. This 3D design is often used, but it hinders and complicates encapsulation.

[0004] MEMS vector scanners are encapsulated and hermetically sealed in a hybrid assembly to adjust their behavior. While the hermetic encapsulation of the vector scanners with a 3D structure, where the actuators and mirror plates are arranged at different heights / levels, provides protection for MEMS components, the MEMS components are still subject to influences from external disturbances, such as particles. Outgassing due to the different manufacturing environments and processes, as well as the necessary transport between manufacturing environments, is also a problem. MEMS components are typically manufactured in a cleanroom, and the subsequent hybrid assembly is carried out in the laboratory using an adhesive.

[0005] What would be desirable is a method for manufacturing a MEMS package or for encapsulating a MEMS structure and a MEMS package that avoids the aforementioned disadvantages and can still be manufactured efficiently and with low errors.

[0006] The object of the present invention is therefore to provide a method for encapsulating a MEMS structure and a MEMS package that enable efficient manufacturing with low errors.

[0007] This problem is solved by the subject matter of the independent patent claims. SENGER F ET AL: "A bi-axial vacuum-packaged piezoelectric MEMS mirror for smart headlights", SPIE PROCEEDINGS; SPIE, US, Vol. 11293, February 28, 2020 (2020-02-28), pages 1129305-1129305, DOI: 10.1117 / 12.2542802, ISBN: 978-1-5106-3673-6 discloses the fabrication of a packaged micromirror in which a base wafer, a functional wafer with the MEMS structure, a frame-shaped structured spacer wafer, and a glass wafer are bonded to form a stacked structure.

[0008] A core idea of ​​the present invention is to provide a spacer structure between a part of a MEMS structure and a lid implemented using a glass wafer for encapsulating a MEMS structure. This enables low processing requirements for the glass wafer, simple positioning of the spacer structure with respect to the MEMS structure, and wafer-level manufacturing, thus enabling efficient encapsulation with low susceptibility to defects.

[0009] According to one variant of the invention, a method for encapsulating a MEMS structure in a stack structure comprises providing a functional wafer structure that at least partially comprises a MEMS structure. To encapsulate the MEMS structure in a stack structure, the functional wafer structure and a glass wafer are further arranged in the stack structure and along a stacking direction relative to one another. The method is carried out such that a cavity in which at least part of the MEMS structure is arranged is closed on one side along the stacking direction with the glass wafer, and such that a spacer structure is arranged between the part of the MEMS structure and the glass wafer in the stack structure in order to provide a distance between the part of the MEMS structure and the glass wafer along the stacking direction, such that the spacer structure encloses part of the cavity.According to the invention, the spacer structure is formed from the functional wafer structure by means of locally selective removal of the functional wafer structure.

[0010] According to another variant of the invention, a method for encapsulating MEMS structures in a stack structure comprises providing a stack structure with a plurality of MEMS regions, such that each MEMS region has a MEMS structure that is at least partially arranged in a MEMS cavity, such that the stack structure has a spacer structure that at least partially encloses each of the cavities of the MEMS regions and provides a distance from the MEMS structure. The method further comprises arranging a glass wafer on the spacer structure by performing a wafer bonding process, such that the cavities on one side of the spacer structure are hermetically sealed by means of the glass wafer. According to the invention, the spacer structure is also formed from the functional wafer structure by locally selective removal of the functional wafer structure.The advantage of this is that by adjusting the distance using the spacer structure, a complex structure of the glass wafer can be eliminated and it can be used simply, efficiently and with few errors already at the wafer level to encapsulate the MEMS structure.

[0011] A MEMS package according to the invention comprises a stack structure comprising a plurality of layers stacked along a stacking direction and having a functional wafer structure comprising a MEMS structure. The MEMS structure is at least partially arranged in a cavity, wherein the cavity forms part of the stack structure. The cavity is bounded on one side along the stacking direction by a glass layer, which is spaced from the MEMS structure by a spacer structure along the stacking direction. According to the invention, the spacer structure is also formed from the functional wafer structure by locally selective removal of the functional wafer structure.

[0012] Further advantageous embodiments are the subject of dependent patent claims.

[0013] Particularly preferred embodiments are explained below with reference to the accompanying drawings. They show: Fig. 1 is a schematic flow diagram of a method according to an embodiment; Fig. 2 is a schematic flow diagram of a method according to an embodiment, which, for example, comprises at least part of a step of the method from Fig. 1 can implement; Fig. 3 a schematic flow diagram of a further method according to an embodiment, which alternatively or additionally implements at least part of a step of the method from Fig. 1 and, for example, alternatively or in addition to the procedure from Fig. 2 can be carried out; Fig. 4 is a schematic side sectional view of an exemplary functional wafer in connection with embodiments described herein; Fig. 5 is a schematic side sectional view of a further functional wafer structure according to an embodiment; Fig. 6 is a schematic side sectional view of a stack structure which can be formed by joining the functional wafer structures of Fig. 4 and Fig. 5 can be obtained; Fig. 7 is a schematic side sectional view of a wafer structure according to an embodiment, which can be used, for example, as a bottom or lid wafer; Fig. 8 is a schematic side sectional view of a stack structure according to an embodiment, which consists of a processed version of the stack structure from Fig. 6 and the wafer structure Fig. 7 can be obtained; Fig. 9 is a schematic side sectional view of a stack structure according to an embodiment, which can be obtained by combining the stack structure of Fig. 8 with a glass wafer; and Fig. 10 is a schematic side sectional view of a stack structure according to an embodiment, which can be obtained by further processing the stack structure from Fig. 9 can be obtained.

[0014] Before exemplary embodiments of the present invention are explained in more detail below with reference to the drawings, it is pointed out that identical, functionally equivalent or equivalent elements, objects and / or structures in the different figures are provided with the same reference numerals, so that the description of these elements shown in different exemplary embodiments is interchangeable or can be applied to one another.

[0015] The embodiments described below are described in conjunction with numerous details. However, embodiments may also be implemented without these detailed features. Furthermore, for clarity, embodiments are described using block diagrams instead of detailed illustrations. Furthermore, details and / or features of individual embodiments may be readily combined with one another, unless explicitly described otherwise.

[0016] The following embodiments relate to the encapsulation of a MEMS structure. An exemplary MEMS structure is considered to be a MEMS vector scanner, i.e., a microelectromechanical system (MEMS) that has an optically reflective surface that is deflected using an actuator. An optical source for this purpose can be part of the MEMS, but this is not required for the consideration of the present invention. An exemplary light source is, for example, a laser or another source of electromagnetic radiation in the visible or non-visible wavelength range. Although vector scanners are generally operated non-resonantly, the present invention is not limited to this.Rather, other MEMS, such as resonantly operated MEMS, can also be encapsulated using the methods described herein, and / or MEMS with other moving elements or possibly no moving elements at all can also be encapsulated. Encapsulation of MEMS structures can also be relevant for other areas where, for example, a reference atmosphere needs to be sealed against external influences. This could include, for example, optical regions or regions for measuring a change in the reference atmosphere.

[0017] The following exemplary embodiments relate to the encapsulation of a MEMS structure. This can be single-layer or multi-layer and comprise semiconductor materials, such as silicon-based, potassium arsenite, or the like. However, exemplary embodiments are not limited to inorganic semiconductors, but can also be readily applied to organic semiconductors, such as organometallic semiconductors.

[0018] MEMS structures can comprise semiconductor materials that exhibit electrically insulating properties under the influence of further processing steps, for example silicon oxide or silicon nitride, which are made electrically conductive in some areas, for example by doping, and which are functionalized by arranging additional layers, whereby a local selective removal of layers can also be considered.

[0019] Fig. 1 shows a schematic flow diagram of a method 100 according to an embodiment. The method 100 can be used to encapsulate a MEMS structure in a stack structure, which means that the MEMS structure is arranged in the stack structure. The method 100 comprises a step 110 in which a functional wafer structure is provided, which at least partially comprises the MEMS structure. Functional at this point can be understood as an electrical function, which means electrical conductivity and / or insulation and / or mechanical movement. The wafer structure can comprise one or more functional wafers, which will be explained in more detail later.

[0020] A step 120 comprises arranging the functional wafer structure and a glass wafer in the stack structure and along a stacking direction relative to one another, meaning that the glass wafer and the functional wafer structure are arranged together in the stack structure. For example, the glass wafer can be bonded to the layers of the wafer structure or to an already formed stack structure with the wafer structure by means of wafer bonding. The method 100 is carried out such that a cavity in which at least a portion of the MEMS structure is arranged is closed on one side along the stacking direction with the glass wafer, for example, hermetically sealed, and such that a spacer structure is arranged between the portion of the MEMS structure and the glass wafer in the stack structure in order to provide a distance between the portion of the MEMS structure and the glass wafer along the stacking direction, such that the spacer structure encloses a portion of the cavity.This is illustrated in step 130. At least parts of step 130 can be performed as a separate step of method 100 or as part of other steps, for example, step 120. A result of method 100 can be a MEMS structure having the spacer structure on at least one side along the stacking direction, which does not exclude intervening layers. The spacer structure can be single-layer or multi-layer and can provide part of the structure for the glass wafer enclosing the cavity.

[0021] Fig. 2 shows a schematic flow diagram of a method 200, which can, for example, implement at least part of step 110 of method 100. A step 210 includes providing a first functional wafer. A step 220 includes providing a second functional wafer. In a step 230, wafer bonding of the first functional wafer and the second functional wafer to each other can be performed by means of a wafer bonding process.

[0022] Method 200 is a possible embodiment of step 110. Multilayer functional wafer structures can be manufactured or provided by method 200. Alternatively or additionally, step 110 can also comprise etching out of an entire layer sequence of successively grown layers, or the like. Alternatively or additionally, step 110 can also be performed by supplying the functional wafer structure.

[0023] Fig. 3 shows a schematic flow diagram of a method 300 according to an embodiment, which can alternatively or additionally carry out at least a part of step 110 and can, for example, be carried out alternatively or in addition to the method 200 or can at least further develop it.

[0024] In a step 310, a first functional wafer may be provided, comprising a first segment of a movable element of the MEMS structure. Furthermore, a second functional wafer may be provided, comprising a second segment of the movable element of the MEMS structure and at least one spacer layer, which at least partially form a stack with the second segment. Step 310 may, for example, provide steps 210 and 220.

[0025] In a step 320, the first functional wafer and the second functional wafer can be wafer bonded to each other using a wafer bonding process. This allows the first segment and the second segment to be connected to each other to at least partially form the movable element of the MEMS structure. Step 320 can at least partially provide step 230.

[0026] In a step 330, a locally selective removal of the spacer layer can be performed after the wafer bonding process and in a first region of the second segment to expose the second segment. The locally selective removal can be performed such that the spacer structure is at least partially formed while retaining at least a portion of the spacer layer in a second region that surrounds the first region. This means that a segment of the movable structure can be removed from the spacer layer and the spacer layer can be retained simultaneously, for example, when method 300 is performed.

[0027] Fig. 4 shows a schematic side sectional view of an exemplary functional wafer 40 in connection with embodiments described herein. The wafer structure 40 may comprise one or more substrate layers 12 1 , 12 2 and / or further substrate layers. An intermediate layer 14 1 may possibly be arranged between substrate layers 12 1 and 12 2 . This may, for example, comprise an oxide layer and / or a nitride layer, may comprise a single layer, or may also have a multi-layer composite system. A function of the intermediate layer 14 may, for example, comprise connecting the substrate layers 12 1 , 12 2 , it may provide electrical conductivity or electrical insulation, but it may also provide another function, for example implementing an etch stop layer or the like.

[0028] The wafer structure 40 can optionally have one, two, or more actuator structures 16 1 and 16 2 , which may be configured to deflect a deflectable region 18 in a later MEMS. The actuator structures 16 1 and 16 2 can, for example, comprise piezoelectric functional layers, thermomechanical or thermoelectric functional layers, comprise magnetoactive materials, or provide any other actuating principle. Alternatively or additionally, sensory materials can also be arranged at the location of the actuator structures 16 1 and / or 16 2 or at other locations, for example, to evaluate a movement of the deflectable region 18. It is possible, but not necessary, for the deflectable region 18 to be implemented at all.

[0029] For electrical contacting of an active or sensor-functional material, one or more electrical conductor structures 22 can be arranged, which can be electrically controlled, for example, via an electrical contact 24. This means that the electrical contact 24 and the electrical conductor 22 can be electrically connected to one another in a sectional plane (not shown) of the wafer structure 40. Likewise, the deflectable region 18 and an outer region 24 of the wafer structure 40 can be connected to one another via one or more mechanical elements, for example spring elements, in order to suspend or support the deflectable region 18 relative to the outer region 24.

[0030] Between the elements 16 1 and 16 2 , which are formed as piezoelectric actuators, on the one hand, and further substrate layers 12 1 and / or 12 2 , intermediate layers can be arranged, for example an electrically insulating intermediate layer 14 2 .

[0031] In other words, Fig. 4 a representation of a first functional wafer, in the case of a MEMS vector scanner, for example, the actuator wafer. In Fig. 4 at least some of the functional parts of the component are shown, for example to realize the desired movement.

[0032] Fig. 5 shows a schematic side sectional view of a functional wafer structure 50 according to an embodiment. The functional wafer structure 50 may comprise one or more substrate layers 12s and 124, wherein a smaller or larger number of substrate layers is also possible. Just as the substrate layers 121 and 122 of Fig. 4 the substrate layers 12 3 and 12 4 may comprise the same or different materials.

[0033] One or more of the substrate layers 12 3 and 12 4 can be structured into subregions, as shown by way of example for the substrate layer 12 4, which is separated from the substrate layer 12 3 by an intermediate layer 14 3 or provides a mechanical connection between these layers. The substrate layer 12 4, either on its own or in conjunction with further layers, such as the layer 14 3 or another layer, can later provide a function of the MEMS, for example the function of a mirror surface. In the context of the exemplary embodiment of the production or encapsulation of a MEMS vector scanner, the functional wafer structure 50 can be understood, for example, as a mirror wafer. In other words, Fig. 5 a second functional wafer, in the case of a MEMS vector scanner, the mirror wafer. Depending on the type of MEMS component, one functional wafer, two functional wafers, or possibly a higher number can be hermetically encapsulated using the methods described herein.

[0034] By providing or producing the functional wafer structure 40, for example, step 110 or 120 can be performed. By manufacturing, producing, or providing the functional wafer structure 50, the other of steps 110 and 120 or 210 and 220 can be performed, for example.

[0035] With reference to method 300, step 310 can, for example, be carried out such that wafer structure 40 is provided as the first functional wafer and wafer structure 50 is provided as the second functional wafer. The deflectable region 18 of the functional wafer structure 40 can, for example, comprise or provide a movable element of the MEMS structure, or at least form a part thereof. A part of layer 124 of the functional wafer structure 50, in contrast, can provide a second segment of the movable element of the MEMS structure. As will be explained below, a spacer layer can be formed from layer 123, which can be used in the subsequent MEMS.

[0036] The substrate layer 124 can, for example, have an inner region 28, for example by introducing one or more trenches 32 into the layer. Alternatively or additionally, one or more connection points 341, 342 and / or 34s can be arranged, which can provide a mechanical connection to an adjacent layer during a later connection process, for example a wafer bonding process. For example, a silicon oxide or a silicon nitride material can be used for this purpose. Alternatively, any other material can be arranged for wafer bonding. It is possible, but not necessary, for the connection points 341 to 343 to be arranged entirely on the functional wafer structure 50; alternatively or additionally, they can also be arranged entirely or partially on the functional wafer structure 40.

[0037] This means that the functional wafer structures 40 and / or 50 can also be implemented in any other way.

[0038] Fig. 6 shows a schematic side sectional view of a stack structure 60, which can be obtained by joining the functional wafer structures 40 and 50. By means of a wafer bonding process, for example, within the scope of step 320, step 230, and / or step 110 as a whole. As a result, the substrate layers 12 1 , 12 2 , 12 3 , and 12 4 can be a common part of the stack structure 60 and arranged along a stacking direction 36.

[0039] Furthermore, the inner region 28 of the functional wafer structure 50 is structured into a plurality of subsegments 28 1 , 28 2 , and 28 3 . The segment 28 2 , together with the deflectable region 18, can later form at least part of a deflectable mirror.

[0040] In other words, in the case of a vector scanner, the mirror wafer 50 can be bonded to the actuator wafer 40. Thus, the functional part can consist of one or two wafers.

[0041] Fig. 7 shows a schematic side sectional view of a wafer structure 70 according to an embodiment. This comprises, for example, a single substrate layer 12s, although alternatively, a larger number of substrate layers may be arranged, which may be integrally connected to one another or connected to one another by means of intermediate layers. The substrate layer 12s may be planar on one or both opposite main sides or structured on one or both main sides. The wafer structure 70 may be arranged in the stack 60 to form part of the stack structure as a boundary wafer structure.

[0042] For example, trenches 32 1 and 32 3 arranged on a main side 12 5 A can contain markings for later dicing or separating wafer segments. One or more depressions or recesses can also be arranged on an opposite main side 12 5 B. A recess 37 on side 12 5 B can, for example, be adapted to a movement of one or more segments of a later MEMS structure. The recess is preferably introduced into a single layer or semiconductor layer, i.e., side walls of the recess 37 are preferably arranged in the same layer as a base surface.

[0043] In other words, Fig. 7 A bottom wafer, which can be used if a cavity is provided. The bottom of the cavity can represent a lower limit of the hermetic encapsulation.

[0044] Fig. 8 shows a schematic side sectional view of a stack structure 80 according to an embodiment, which consists of a machined version 60' of the stack structure 60 of Fig. 6 and the wafer structure 70 from Fig. 7 can be obtained, for example, by connecting the stack structure 60' or 60 to one another by means of a connecting region 34 4 and / or 34 5 , for example by a wafer bonding process. For example, the regions 34 4 and 34 5 can form a circumferential region, so that a hermetically sealed connection is established between the stack structure 60 or 60' and the wafer structure 70. This wafer bonding process can take place in the same process environment or the same process chamber as, for example, the connection of the wafer structures 40 and 50.

[0045] The stack structure 60' can be further processed compared to the stack structure 60. While the "mirror element" and "movable post" segments are joined together, for example, by connecting the wafer structures 40 and 50, for example by performing step 320, a movable element 38 of the stack structure 80 can be exposed by locally selective removal of the substrate layer 12 3 , approximately opposite the region 28 2 . In outer regions, the substrate layer 12 3 can remain and function, for example, as a spacer layer to set a distance A to the movable element 38, in particular for further, additional layers. The layer 12 3 can thus, as a spacer structure, set and at least partially provide a distance A between the MEMS structure or components thereof and a later cover layer.The distance A can be adapted to an intended volume of a later cavity and / or to a movement amplitude of movable components of the MEMS structure.

[0046] In other words, according to the Fig. 8 compared to the Fig. 6 and 7 The stack of functional wafers is bonded back to the base wafer. This allows the functional wafer to maintain or maintain a certain distance above the lid wafer.

[0047] Fig. 9 shows a schematic side sectional view of a stack structure 90 according to an embodiment, which is obtained by combining the stack structure 80 from Fig. 8 with a glass wafer 42. This can be arranged, for example, as a cover or at least as part thereof on the stack structure 80, so that a cavity 44, in which the movable element 38 is movably arranged, is hermetically sealed, on the one hand by the substrate layers 12 5 or the base wafer and, on the other hand, by the glass wafer 42. The glass wafer 42 can also be arranged on the stack structure 80 by means of a bonding process. This can, for example, ensure that the process chamber does not have to be left for locally selective etching and / or for wafer bonding for the encapsulation of the movable element 38, or at least that the clean room environment can be maintained without requiring increased effort.

[0048] It should be noted that, as with other steps in the methods described herein, the sequence presented is merely exemplary and can also be modified. For example, the wafer structure 70 can also be bonded to the wafer structure 40 before the structures 40 and 50 are bonded; and / or the glass wafer can be bonded to the wafer structure 50 before or after the wafer structure 70 is arranged and / or possibly even before the wafer structures 40 and 50 are bonded. A different order of the bonding steps can be advantageous, particularly with a different design of the wafer structures or MEMS, but this does not impair the use of a spacer structure and a glass layer.

[0049] The illustrated sequence of bonding layers or layer sequences is purely exemplary. It is also possible, for example, to bond the glass wafer 42 prior to bonding the wafer structure 50 or a processed version 50' thereof, in which, for example, the layer 123 is locally selectively removed.

[0050] The cavity 44 can be hermetically sealed in the illustrated but also in other step sequences by arranging the functional wafer structure 50 or 50' and the glass wafer 44 in the stack structure using a wafer bonding process. On a side of the MEMS structure 46 opposite the glass wafer 42, which, for example, has the movable element 38, a confinement wafer structure, the layer 12 5 , can form part of the stack structure by means of a further wafer bonding process before or after the wafer bonding for connecting the glass wafer, so that the glass wafer 42, on the one hand, and the confinement wafer structure 12 5 , on the other hand, close the cavity 44 along the stacking direction 36. The functional wafer structure 40 / 50 and the spacer layer 12 3 can close the cavity 44 perpendicular to the stacking direction 36.

[0051] As it is related to the Fig. 7 As described, the boundary wafer structure 125 can be structured on a side facing the MEMS structure 46 to have a recess in a region opposite the MEMS structure 46. This recess can, for example, be adapted to a movement of the movable element 38 of the MEMS structure 46.

[0052] The recess 37 can be defined by a single semiconductor layer of the confinement wafer structure 70. This means that the recess 37 is formed, for example, by a locally selective etching process or the like within a single layer, which differs from a multilayer structure where, for example, wall structures are created by additional layers. Implementation as a single layer with a recess offers the advantage of a simple and precise definition of the cavity 44.

[0053] The glass wafer 42 can be planar entirely or at least in a region arranged opposite the MEMS structure 46 or the movable element 38. The spacing can nevertheless be provided by means of the spacing structure 123. This avoids the complex production of a three-dimensional glass body as a glass cap or CAP, while still allowing the advantages of using glass material to be utilized.

[0054] According to one embodiment, the method is carried out such that the cavity 44 is hermetically sealed and a pressure different from atmospheric pressure or ambient pressure is provided in the cavity. This can be easily achieved in process chambers for wafer bonding, unlike on laboratory benches for the classic bonding of multiple layers. Embodiments provide for the generation of a negative pressure in the cavity. Other embodiments provide for the generation of an overpressure in the cavity, for example a pressure of at least 1.5 bar, 1.8 bar or at least 2 bar, or even higher pressures, for example 3 bar. An overpressure makes it possible to decelerate a movement of the movable element 38. This is particularly relevant for structures that are driven non-resonantly and makes it possible, for example, to reduce or avoid overshoot beyond a desired position.

[0055] By adjusting the pressure during the bonding of layers, it is also possible to avoid depositing getter material in a specific area of ​​the cavity. Such a getter material is deposited in known processes to allow pressure adjustment, for example, to create a vacuum later. Since this can now be done during wafer bonding, the deposit of such a material is still possible, but the need for it is reduced or even eliminated.

[0056] A movable element 38 is arranged in the stack structure 90. Furthermore, an actuator is provided to deflect the movable element 38 from a rest position, which is influenced, for example, by spring elements or the like. For example, the movable element 38 comprises a mirror structure.

[0057] The MEMS structure can be designed such that the movable element 38 is controlled below a mechanical resonant frequency of a spring-mass system. The movable element 38 can provide part of the mass of such a spring-mass system. A spring suspension can provide a spring component, both of which together influence a resonant frequency. While in resonance-operated mirrors, for example, the springs are softly suspended to enable resonant operation, structures for non-resonant operation require a significantly higher spring stiffness.

[0058] As is the case, for example, in connection with the Fig. 8 and in connection with the Fig. 9 As further illustrated, by means of the locally selective removal, for example by carrying out step 330 to remove a portion of the spacer layer 12 3 after a wafer bonding process, this can be used at the same time to expose a corresponding segment of the MEMS structure 46 and thus to enable a later movement of the movable element 38. This can be done while retaining at least a portion of the spacer layer 12 3 in, for example, the outer region of the cavity 44, so that the region from which the layer 12 3 is removed is enclosed by the remaining portion and at least partially forms the spacer structure. This does not preclude the layer 12 3 from being thinned locally in an outer region to adjust the distance or from being further structured.

[0059] In other words, Fig. 9 A schematic representation of the third wafer bonding step, in which a lid wafer is assembled with the existing wafer stack, creating a hermetically sealed cavity 44 in the center. Within this cavity, it is also possible to set a defined pressure and / or a defined atmosphere composition, allowing both negative pressure (technical vacuum), atmosphere, and positive pressure to serve as the working environment for the MEMS component. Positive pressure can be used to dampen post-oscillations resulting from a movement of the MEMS component.

[0060] Fig. 10 shows a schematic side sectional view of a stack structure 90' ​​according to an embodiment, which can be obtained by further processing of the stack structure 90 from Fig. 9 can be obtained. For example, an additional metallization 48 can be provided to electrically contact the actuator structures 16 1 and / or 16 2 .

[0061] Such steps are optional. According to one embodiment, a method according to the invention comprises separating the stack structure into a plurality of MEMS packages, for example, into a region of the trenches 32 2 and / or 32 3 .

[0062] Embodiments are directed to providing the spacer layer 12 3 from a semiconductor material, although this is not mandatory even if certain advantages are obtained thereby, in particular with regard to MEMS manufacturing.

[0063] In other words, a bottom wafer can optionally be metallized to establish electrical contact with the MEMS component. The glass frit, i.e., the interface between the spacer structure 123 and the glass wafer 42, can be electrically conductive to alternatively or additionally establish electrical contact with the MEMS component.

[0064] According to one embodiment, a method comprises processing the functional wafer structure 40 and / or 50 in a process chamber and closing the cavity in the process chamber. Embodiments allow for a different sequence of bonding processes, sometimes even simultaneously, wherein sequential bonding processes can be carried out in the same or a different process chamber. For example, the wafer structure 40 can be Fig. 4 and the wafer structure 50 from Fig. 5 and the structure 70 from Fig. 7 prepared and possibly fully structured and the three wafers can be bonded together simultaneously in one step, enabling rapid processing.

[0065] However, it may be simpler to first bond the wafer structures 40 and 50 together, then etch or expose the mirror plate, and then subsequently bond them together with the wafer structure 70. According to one embodiment, which can be carried out alternatively or in addition to the method 100, to encapsulate a MEMS structure in a stack structure, a stack structure is provided with a plurality of MEMS regions, such that each MEMS region has a MEMS structure that is at least partially arranged in a MEMS cavity, such that the stack structure has a spacer structure that at least partially encloses each of the cavities of the MEMS regions and provides a distance from the MEMS structure.Furthermore, a glass wafer, such as wafer 42, is arranged on the spacer structure by performing a wafer bonding process, so that the cavities on one side of the spacer structure are hermetically sealed by means of the glass wafer. For example, a wafer structure with several, i.e., multiple-use or layer stacks 80 provided at the wafer level can be arranged and simultaneously sealed by the glass wafer 42 on at least one side by means of wafer bonding.

[0066] Although the method described herein is described as using the wafer structure 70 to seal a side opposite the glass wafer 42, this is not provided in all embodiments. For example, a continuous substrate layer may be used that is part of the wafer structure 40 and already provides a sealing of the cavity on this side. Alternatively or additionally, it is possible to omit the sealing of the cavity on this side or to perform it at a later time.

[0067] A MEMS package according to one embodiment, which can be obtained, for example, by singulating the stack structure 90 or 90', but can also have any other MEMS structure, comprises a stack structure comprising a plurality of layers stacked along the stacking direction 36, and a functional layer structure comprising a MEMS structure, for example the MEMS structure 46. The MEMS structure is at least partially arranged in a cavity, for example the cavity 44, which has the movable element 38. The cavity is delimited on one side along the stacking direction by a glass layer, which is spaced from the MEMS structure by a spacer layer along a stacking direction.

[0068] Embodiments provide hermetic encapsulation at the wafer level, which is particularly, but not exclusively, advantageous for quasi-static MEMS components, such as MEMS vector scanners, where any resonance behavior must be avoided. Wafer-level hermetic encapsulation not only protects the MEMS components from environmental influences such as dust, moisture, vibration, and the like, but also allows a defined internal pressure within the encapsulation, allowing the behavior of the MEMS components to be independent of the ambient pressure.

[0069] To implement hermetic encapsulation through wafer bonding, three to four wafers or wafer structures are used in the exemplary embodiments. These are explained in conjunction with the figures described herein. In the examples, a MEMS vector scanner is encapsulated as an example, although the principle is also transferable to other MEMS devices.

[0070] Embodiments can be implemented independently of structures, sizes, and drive principles. MEMS components can be hermetically encapsulated at the wafer level using the described methods to protect them from the environment. These embodiments are particularly advantageous when using one or two functional wafer structures. In the cavity, not only negative pressure (technical vacuum, i.e., down to technically feasible low pressures) but also positive pressure can be set. With positive pressure, the Q factor, i.e., the damping, of the movement of the MEMS components can be reduced, so that the post-oscillation can be significantly damped or eliminated.

[0071] Embodiments can be applied in the manufacture of MEMS components, such as a vector scanner.

[0072] Embodiments relate to a wafer stack in which three to four wafers can be bonded together and which has a functional MEMS component as well as a bottom wafer and a lid wafer, so that the centrally arranged MEMS component can operate in a closed cavity under a defined pressure.

[0073] According to one embodiment, vacuum, atmosphere, but also overpressure can be set as the working pressure for the component in the cavity from the protective function in order to increase or decrease the quality factors.

[0074] According to one embodiment, the bottom wafer can be metallized to realize the electrical contact to the MEMS component.

[0075] According to an alternative or additional aspect, the glass frit may be electrically conductive to realize the electrical contact to the MEMS component.

[0076] Although some aspects have been described in connection with a device, it is understood that these aspects also represent a description of the corresponding method, so that a block or component of a device can also be understood as a corresponding method step or as a feature of a method step. Similarly, aspects described in connection with or as a method step also represent a description of a corresponding block, detail, or feature of a corresponding device.

[0077] The above-described embodiments are merely illustrative of the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be apparent to others skilled in the art. Therefore, it is intended that the invention be limited only by the scope of the following claims and not by the specific details presented in the description and explanation of the embodiments herein. literature

[0078] [1] "Variants of Hermetic Packages for LiDAR Sensors | SCHOTT". / engb / products / hermetic-packages-for-lidar-sensors / product-variants (zugegriffen Sep. 21, 2020). [2] "Mirrorcle Technologies MEMS Mirrors - Technical Overview", 2013. https: / / www.semanticscholar.org / paper / Mirrorcle-Technologies-MEMS-Mirrors-%E2%80%93- Technical / d131 a1576787ffa47fbd035881 ec3780cf1 a09b4 (zugegriffen Sep. 21, 2020). [3] S. Gu-Stoppel u. a., "AlScN based MEMS quasi-static mirror matrix with large tilting angle and high linearity", Sens. Actuators Phys., Bd. 312, S. 112107, Sep. 2020, doi: 10.1016 / j.sna.2020.112107.

Claims

1. Method for encapsulating an MEMS structure in a stack structure including several layers stacked along a stacking direction, comprising: providing (110) a functional wafer structure including at least partly the MEMS structure; arranging (120) the functional wafer structure and a glass wafer (42) in the stack structure and along a stacking direction (36) to each other; such that a cavity (44) in which at least a part of the MEMS structure is arranged is closed on one side along the stacking direction (36) by the glass wafer (42); and such that a spacing structure (123) is arranged between the part of the MEMS structure and the glass wafer (42) in the stack structure to provide a spacing (A) between the part of the MEMS structure and the glass wafer (42) along the stacking direction (36); such that the spacing structure (123) encloses part of the cavity (44), characterized in that the spacing structure (123) is formed of the functional wafer structure by means of local selective removal of the wafer structure.

2. Method according to claim 1, wherein providing the functional wafer structure includes providing a first functional wafer (40) with a mechanical element and a second functional wafer (50) and the method includes wafer bonding the first functional wafer and the second functional wafer with one another by means of a wafer bonding process.

3. Method according to any of the preceding claims, wherein the cavity (44) is hermetically closed by arranging the functional wafer structure and the glass wafer (42) in the stack structure by using a first wafer bonding process; and by a limiting wafer structure forming part of the stack structure on a side of the MEMS structure opposite to the glass wafer (42) by means of a second wafer bonding process, such that the glass wafer (42) on the one hand and the limiting wafer structure on the other hand close the cavity (44) along the stacking direction (36); and the functional wafer structure and the spacing structure limit the cavity (44) perpendicular thereto.

4. Method according to claim 3, wherein the limiting wafer structure is structured on a side facing the MEMS structure and comprises a recess (37) in an area opposite to the MEMS structure.

5. Method according to any of the preceding claims, wherein the glass wafer (42) is formed in a planner manner at least in an area that is arranged opposite to the MEMS structure.

6. Method according to any of the preceding claims, wherein a side of the glass wafer (42) facing the MEMS structure is formed in a planar manner.

7. Method according to any of the preceding claims, which is performed such that the cavity (44) is hermetically closed and a pressure differing from the atmosphere pressure is provided in the cavity (44).

8. Method according to claim 7, wherein a negative pressure is generated in the cavity (44); or wherein an overpressure is generated in the cavity (44).

9. Method according to claim 7 or 8, wherein no getter material is arranged in an area of the cavity (44).

10. Method according to any of the preceding claims, wherein the MEMS structure includes a moveable element (38) and an actuator (161, 162) for deflecting the moveable element (38) from a resting position.

11. Method according to any of the preceding claims, further comprising: locally selectively removing (330) a spacing layer after the wafer bonding process in a first area to expose the functional wafer structure at least partly while maintaining at least a part of the spacing layer in a second area enclosing the first area to at least partly form the spacing structure (123).

12. Method according to any of the preceding claims, wherein providing the functional wafer structure includes: providing (310) a first functional wafer including a first segment of a moveable element of the MEMS structure; and a second functional wafer including a second segment of the moveable element of the MEMS structure and at least a spacing layer that at least partly forms a stack together with the second segment; wafer bonding (320) of the first functional wafer and the second functional wafer with one another by means of a wafer bonding process; such that the first segment and the second segment are connected to one another, to at least partly form the moveable element; wherein the method further comprises: locally selectively removing (330) the spacing layer after the wafer bonding process in a first area of the second segment to expose the second segment while maintaining at least of the spacing layer in a second area enclosing the first area to at least partly form the spacing structure (123).

13. Method according to any of the preceding claims, further comprising: processing the functional wafer structure in a process chamber; closing the cavity (44) in the same process chamber or a different process chamber.

14. Method for encapsulating MEMS structures in a stack structure, comprising: providing a stack structure including several layers stacked along a stacking direction with a functional wafer structure with a plurality of MEMS areas, such that each MEMS area comprises an MEMS structure that is arranged at least partly in an MEMS cavity (44); such that the stack structure comprises a spacing structure (123) enclosing each of the cavities of the MEMS areas at least partly and providing a spacing (A) to the MEMS structure along the stacking direction (36); and arranging a glass wafer (42) on the spacing structure (123) along the stacking direction (36) by performing a wafer bonding process, such that the cavities on one side of the spacing structure (123) are hermetically sealed by means of the glass wafer (42), characterized in that the spacing structure (123) is formed from the functional wafer structure by means of local selective removal of the functional wafer structure.

15. MEMS package, comprising: a stack structure including several layers stacked along a stacking direction (36); and comprising a functional wafer structure including an MEMS structure; wherein the MEMS structure is at least partly arranged in a cavity (44); and the cavity (44) forms part of the stack structure; wherein the cavity (44) is limited on one side along the stacking direction (36) by a glass layer, which is spaced apart from the MEMS structure along the stacking direction (36) by a spacing structure (123), characterized in that the spacing structure (123) is formed from the functional wafer structure by means of local selective removal of the wafer structure.