MEMS device and method for manufacturing the same

Abstract

To provide a microelectromechanical system (MEMS) device and a method of manufacturing such the MEMS.SOLUTION: A MEMS device comprises, in order from bottom to top, a handle layer, a first electrically insulating layer, a first element layer formed by patterning a layer of deposited polycrystalline silicon (poly-Si), a second electrically insulating layer, a second element layer formed by patterning a layer of single crystal silicon (mono-Si), and a cap layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to MEMS devices and methods for producing MEMS devices, and more particularly to MEMS devices with two element layers and methods for manufacturing double layer MEMS devices. [Background technology]

[0002] Microelectromechanical systems (MEMS) devices, which are fabricated using silicon-based technology, are becoming popular. A typical application for MEMS devices is as an inertial sensor that detects acceleration and / or angular rate. This type of MEMS device is widely used in consumer, automotive, and industrial applications.

[0003] Capacitive sensing in MEMS devices is performed by detecting the change in capacitance caused by a change in the distance between two electrodes. Typically, the capacitance is sensed between a movable electrode and one or more stationary electrodes.

[0004] In a typical capacitive MEMS device for inertial sensing, a stationary electrode is mounted on a substrate, such as a handle or cap wafer. For example, a metal electrode can be mounted on the surface of the substrate wafer. The MEMS device is exposed to various stress sources. During component packaging, some manufacturing steps, such as molding, apply pressure to the substrate. Different materials have different thermal properties, and therefore, the substrate may also be subjected to pressure due to differences in thermal expansion of the materials within the MEMS device package. The MEMS device may also be subjected to various external forces that cause changes in the shape of the substrate. The environment in which the MEMS device is used may be subject to large temperature changes, vibrations, shocks, and so on, all of which induce stress on the MEMS device. When the stationary electrode is attached to the substrate, any changes in the substrate morphology caused by stress can also affect the distance between the stationary electrode and the respective movable electrode. This can reduce the accuracy of the capacitive sensing.

[0005] The following description refers to inertial MEMS sensors and their manufacturing issues. However, the present disclosure also applies generally to other types of MEMS devices. For example, a MEMS device may include one or more of the following structures, singly or in combination with each other: an accelerometer, a gyroscope, a geophone, an inclinometer, and a resonator. A MEMS device may also be a MEMS actuator.

[0006] Description of the Prior Art US Patent No. 10,830,590 discloses a microelectromechanical sensor having a substrate including a mechanical functional layer and an electrode device made of single crystal silicon, and a conductive wiring layer having aluminum or tungsten wiring.

[0007] US Patent Application Publication No. 20200156930 discloses a double-sided capacitive sensing MEMS device with a hollow body, which is fabricated by epitaxially growing a polysilicon (poly-Si) structure.

[0008] U.S. Patent No. 9,463,976 discloses a vertically stacked MEMS device wafer assembly for producing an integrated MEMS device having vertically stacked inertial transducer elements, each in a different layer of a multi-layer semiconductor structure, where the different MEMS transducer structures are hermetically shielded from the ambient environment and from each other. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] U.S. Patent No. 10,830,590 [Patent Document 2] US Patent Application Publication No. 20200156930 [Patent Document 3] U.S. Patent No. 9,463,976 Summary of the Invention [Problem to be solved by the invention]

[0010] The object is to provide a method and apparatus for solving the problem of reducing the material costs of MEMS devices while improving the robustness of the MEMS devices with wider gaps between element layers and smaller signal paths. The object of the present invention is achieved by a MEMS device as defined in claim 1. The object of the present invention is further achieved by a manufacturing method as defined in claim 6. [Means for solving the problem]

[0011] Preferred embodiments of the invention are disclosed in the dependent claims.

[0012] According to a first aspect, there is provided a microelectromechanical systems (MEMS) device comprising, in order from bottom to top, i) a handle layer comprising at least one cavity and at least one suspension structure, ii) a first electrically insulating layer, iii) a first device layer formed by patterning a layer of deposited polycrystalline silicon (poly-Si), wherein at least one structural element in the first device layer is suspended by the at least one suspension structure, the at least one structural element optionally comprising at least one vibrating element, iv) a second electrically insulating layer, v) a second device layer comprising at least one vibrating element movably suspended above the first device layer, the second device layer being formed by patterning a layer of single crystal silicon (mono-Si), and vi) a cap layer.

[0013] The handle layer, the first element layer, the second element layer, and the cap layer, as well as the first electrical insulation layer between the handle layer and the first element layer and the second electrical insulation layer between the first element layer and the second element layer, are configured to form walls of a housing that includes at least one vibration element, at least one stationary electrode, and at least one movable electrode for detecting and / or causing movement of the at least one vibration element.

[0014] According to some embodiments, the first device layer comprises at least one polycrystalline silicon (poly-Si) feedthrough extending from the first device layer to the second device layer for electrically coupling structural elements of the first device layer to structural elements of the second device layer and / or to electrical connections provided in the cap layer.

[0015] According to some embodiments, the electrically insulating material in the second electrically insulating layer is removed around the at least one poly-Si feedthrough such that the at least one poly-Si feedthrough is the only mechanical contact between the respective structural elements of the first and second device layers.

[0016] According to some aspects, the first device layer includes at least one stop structure extending toward the second device layer over a distance that is less than a thickness of the second electrically insulating layer.

[0017] According to some embodiments, the MEMS device further comprises a metal bonding layer between the second element layer and the cap layer, the metal bonding layer further configured to form a portion of the wall of the housing.

[0018] According to a second aspect of the present invention, there is provided a method for manufacturing a MEMS device, the method comprising the steps of: i) forming a handle layer from a mono-Si handle wafer, the step of forming the handle layer including forming at least one cavity and simultaneously forming at least one suspension structure on a first surface of the handle layer and covering the first surface of the handle layer with a first electrically insulating layer; ii) forming a second electrically insulating layer on the mono-Si wafer; iii) patterning the second electrically insulating layer; iv) depositing a poly-Si layer on the patterned second electrically insulating layer; and v) forming a first element layer from the first poly-Si layer, the step of forming the first element layer including thinning the first poly-Si layer to a first thickness and forming a plurality of first trenches extending through the first element layer by dry etching. vi) fusion bonding the first device layer onto the first electrical insulating layer on the first side of the handle layer; vii) forming a second device layer from the mono-Si wafer, wherein forming the second device layer comprises thinning the mono-Si wafer to a second thickness, optionally forming at least one recessed region in the second mono-Si wafer, and dry etching a plurality of second trenches extending through the second mono-Si wafer; viii) releasing structural elements of the first and second device layers by removing exposed portions of the first and second electrical insulating layers through thicknesses of the first and second electrical insulating layers with hydrofluoric acid (HF) etching; and ix) encapsulating the structural elements in an enclosure by bonding a cap layer onto the second device layer.

[0019] According to some aspects, the step of patterning the second electrically insulating layer includes removing one or more portions of the second electrically insulating layer throughout the thickness of the second electrically insulating layer, and the step of depositing the poly-Si layer includes filling the removed portions of the second electrically insulating layer with the deposited poly-Si, thereby generating one or more poly-Si feedthroughs extending from the first device layer through the second electrically insulating layer to the second device layer for electrically coupling one or more structural elements of the first device layer and the second device layer.

[0020] According to some aspects, the step of patterning the second electrically insulating layer includes recessing one or more portions of the second electrically insulating layer over a portion of the thickness of the second electrically insulating layer, and the step of depositing the poly-Si layer further includes filling the recessed one or more portions of the second electrically insulating layer to generate one or more poly-Si stop structures extending toward the second device layer.

[0021] According to some aspects, the method further includes forming at least one recessed region in the mono-Si wafer after thinning the first poly-Si layer to the first thickness and before forming the plurality of first trenches extending through the first device.

[0022] According to some aspects, the method further includes bonding the second device layer to the cap layer with a metal bonding layer.

[0023] The present invention is based on the idea of ​​having two suspended element layers within a MEMS device. In this context, we refer to elements that play a role in the function of the MEMS device as structural elements. These structural elements may be fixed, such as support structures, electrical connections, and stationary electrodes. The structural elements in the first element layer are suspended to the handle layer and / or the cap layer via the second element layer by rigid suspension structures such as anchors. The first element layer includes structural elements used as stationary electrodes, and may also be used for electrical routing. Both element layers may include a seismic mass used as a movable electrode and / or a seismic mass coupled to the movable electrode. The second element layer may also include a stationary electrode. As known in the art, suspension of a seismic mass typically includes flexible suspension structures such as springs and beams designed to allow one or more desired directions of motion of the seismic mass while suppressing any undesired directions of motion of the seismic mass. One device layer is made from monocrystalline silicon (mono-Si) and the other device layer is made from polycrystalline silicon (poly-Si). The patterns on the device layers can be fabricated using a silicon-on-insulator (SOI) process that utilizes etching, preferably dry etching such as deep reactive ion etching (DRIE), to define structural elements within the device layers. [Effects of the Invention]

[0024] The present invention provides a two-element layer structure that improves the accuracy of MEMS devices by providing a mechanically stable structure within the MEMS device that is robust against stress deformation, while the device structure of the present invention also has the advantage of facilitating high design flexibility and a small die area. Because both the moving electrode and the stationary electrode can be mounted mechanically isolated from the substrate (handle layer and cap layer), stresses affecting the substrate do not cause changes in the geometry of the structural elements within the element layer. Sensitivity to stress can be further improved by laterally suspending both element layers on a common anchor location. According to some embodiments, a dual silicon element layer design can be designed and manufactured without the need for drilling holes in the vibrating element and / or other structural elements within the element layer, thus avoiding the capacitance and mass reduction caused by such drilling, thereby promoting higher capacitance and therefore improved sensitivity of the MEMS device. While poly-Si element layers may be considered inferior in some technical characteristics compared to mono-Si element layers, poly-Si element layers are often cheaper to manufacture, depending on the thickness of the poly-Si layer. Therefore, MEMS devices according to embodiments of the present invention are more cost-effective than MEMS devices that include two mono-Si device layers. Furthermore, the properties of the two different silicon layers allow for improved design freedom compared to using only a mono-Si device layer. [Brief explanation of the drawings]

[0025] In the following, the invention will be explained in more detail in connection with preferred embodiments with reference to the accompanying drawings. [Figure 1] 1 is a cross-sectional view of a MEMS device according to a first embodiment. [Figure 2] FIG. 4 is a cross-sectional view of a MEMS device according to a second embodiment. [Figure 3] FIG. 10 is a cross-sectional view of a MEMS device according to a third embodiment. [Figure 4] FIG. 10 is a cross-sectional view of a MEMS device according to a fourth embodiment. [Figure 5a] 1A to 1C are diagrams illustrating a method for manufacturing a MEMS device. [Figure 5b] 1A to 1C are diagrams illustrating a method for manufacturing a MEMS device. [Figure 5c] 1A to 1C are diagrams illustrating a method for manufacturing a MEMS device. [Figure 5d] 1A to 1C are diagrams illustrating a method for manufacturing a MEMS device. [Figure 5e] 1A to 1C are diagrams illustrating a method for manufacturing a MEMS device. [Figure 5f] 1A to 1C are diagrams illustrating a method for manufacturing a MEMS device. [Figure 5g] 1A to 1C are diagrams illustrating a method for manufacturing a MEMS device. [Figure 5h] 1A to 1C are diagrams illustrating a method for manufacturing a MEMS device. [Figure 5i] 1A to 1C are diagrams illustrating a method for manufacturing a MEMS device. [Figure 5j] 1A to 1C are diagrams illustrating a method for manufacturing a MEMS device. [Figure 6a] 10A-10C illustrate the generation of stopper structures in a manufacturing method. [Figure 6b] 10A-10C illustrate the generation of stopper structures in a manufacturing method. [Figure 6c] 10A-10C illustrate the generation of stopper structures in a manufacturing method. DETAILED DESCRIPTION OF THE INVENTION

[0026] Single-crystal silicon (mono-Si), also known as monocrystalline silicon, is a well-known base semiconductor material for silicon-based discrete components and integrated circuits. Mono-Si consists of silicon with a continuous, solid crystalline lattice throughout. Due to its excellent mechanical strength and resilience, as well as the wide variety of standard processes available, mono-Si is the material of choice for robust MEMS devices. It is well known in the art that in MEMS devices, mono-Si layers are used as conductors and are doped to make them conductive for that purpose. For example, boron-doped P-type silicon wafers are common, while phosphorus (P)-doped N-type wafers are also used in some specialized applications.

[0027] In this context, polysilicon, also known as polycrystalline silicon or bicrystalline silicon, refers to silicon composed of small crystals known as crystallites. Like monocrystalline silicon, polycrystalline silicon can be doped to become conductive. Polycrystalline silicon contains crystals with different orientations relative to one another. Therefore, its elastic constants do not depend on the geometry and / or orientation as they do in monocrystalline silicon. Polycrystalline silicon does not contain oxygen, as monocrystalline silicon crystals grown by the Czochralski (CZ) method do. Furthermore, the properties of polycrystalline silicon are easier to tune. For example, its conductivity can be easily adjusted by doping, and highly doped polycrystalline silicon is easier to achieve than monocrystalline silicon.

[0028] In this context, silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula SiO2. Silicon dioxide is an electrical insulator.

[0029] In the following description, for convenience, the upward direction refers to the positive z-axis direction and the downward direction refers to the negative z-axis direction. It should be understood that these directions should not be interpreted as limiting the use position of the MEMS device. A simplified MEMS device will have only a limited number of structural elements, such as anchors, beams, electrical contacts, masses, and / or limiters, often only one of each. It will be understood by those skilled in the art that an actual MEMS device can include two or more of any of such structural elements in any combination.

[0030] Figure 1 shows a cross section of a MEMS device according to a first embodiment. The drawing is not to scale.

[0031] Starting from the bottom of the MEMS device 100, the first layer is a handle layer 10 made of mono-Si. The handle layer 10 comprises at least one cavity 11. Within the cavity 11 there is at least one suspension structure 12, also known as an anchor. The at least one cavity 11 is preferably formed as a saucer that does not reach the sides of the handle layer 10, so that walls 13 are provided within the handle layer 10 at least around its periphery. The at least one cavity 11 increases in distance from the bottom of the cavity 11 towards the first element layer 20 above the handle layer 10. This increase in distance reduces the risk of vibration elements in the first element layer 20 coming into mechanical contact with the handle layer 10 and reduces undesirable parasitic capacitance between the handle layer 10 and structural elements in the superimposed first element layer 20.

[0032] Between the handle layer 10 and the first element layer 20 is an electrical insulating layer 15. Most of the sacrificial electrical insulating layer 15 is removed during the fabrication process, but as can be seen in FIG. 1 , a portion of the electrical insulating layer 15 remains between the handle layer 10 and the first element layer 20. The electrical insulating layer is preferably made from silicon dioxide. The electrical insulating layer 15 facilitates bonding between the handle layer 10 and the first element layer 20, forms part of the wall of the housing in which all structural elements of the MEMS device are encapsulated, and is also used as a sacrificial layer during fabrication, supporting and protecting the structure during the fabrication process before being removed.

[0033] The first device layer 20, made of poly-Si, includes structural elements mechanically suspended on suspension structures 12 provided on the handle layer 10 and / or by suspension structures 32 provided on the second device layer 30, which transmit the suspension to the cap layer 40. The structural elements on the first device layer 20 may be fixed or vibrating. Vibrating structural elements refer to elements configured to move in response to physical phenomena such as pressure, acceleration, or angular velocity. The thickness of the poly-Si layer can be designed based on the requirements set by the type of structural element therein. The structural elements on the first device layer 10 are advantageously used as fixed or vibrating elements 21, such as electrodes of a capacitive electrode pair that can be used for either sensing or actuation purposes. Another possible use of the structural elements on the first device layer 10 is signal routing, as illustrated by the signal-carrying beam 24 that can move between the vibrating element 31 on the second device layer 30 and the cavity 11. To reduce unwanted capacitance between the vibrating element 31 and the signal carrying beam 24, the signal carrying beam 24 is preferably narrow in the lateral (x-axis) dimension so that the overlap area between the two is small.

[0034] The first element layer 20 preferably comprises a frame portion 23 which surrounds the structural elements of the first element layer 20 and forms part of the outer wall of the housing which comprises the structural elements of the MEMS device.

[0035] Because the structural elements on the first element layer 20 are only supported relative to the handle layer 10 by separate suspension structures 12, 32 and / or relative to the cap layer 40 via the second element layer 30, the structural elements on the first element layer 20 are less susceptible to stresses affecting the MEMS device 100, and deformation of the cap layer 40 or handle layer 10 due to stress results in less deformation or displacement of the structural elements on the first element layer 20, and therefore less change in distance occurs between the structural elements of the first element layer and the structural elements of the second element layer 30 due to mechanical stresses affecting the MEMS device 100.

[0036] Above the first element layer 20 is a second element layer 30 that includes the vibrating element 31 of the MEMS device 100. To facilitate vibratory motion, the second element layer 30 can be made thicker than the first element layer 20, thereby increasing the mass of the vibrating element 31.

[0037] Between the first device layer 20 and the second device layer 30 is an electrical insulating layer 25. Most of the electrical insulating layer 25 is removed in the fabrication process, but as can be seen in FIG. 1 , a portion of the electrical insulating layer 25 remains between the first device layer 20 and the second device layer 30. The electrical insulating layer 25 is preferably made from silicon dioxide. The electrical insulating layer 25 facilitates bonding between the first device layer 20 and the second device layer 30, forms part of the wall of the housing in which all structural elements of the MEMS device are encapsulated, and is also used as a sacrificial layer during fabrication, supporting and protecting the structure during the fabrication process before being removed.

[0038] Poly-Si feedthroughs 28 extending from the first element layer 20 provide electrical connection across the electrical insulation layer 25 between the first element layer 20 and the second element layer 30, allowing electrical signals to be carried to and from the first element layer 20.

[0039] The second device layer 30 is made from mono-Si and includes a vibrating element suspended indirectly via the first device layer 20 on a suspension structure 12 provided on the handle layer 10 and / or by a rigid suspension structure 32 in the second device layer 30 suspended on the cap layer 40. As known in the art, the suspension is provided by springs and / or flexible beams (not shown) to allow movement of the vibrating element 31.

[0040] The second element layer 30 preferably comprises a frame portion 33 that surrounds the structural elements of the second element layer 30 and forms part of the outer wall of the housing that comprises the structural elements of the MEMS device 100 .

[0041] The structural portions of the first device layer 20 and the second device layer 30 are encapsulated in an enclosure between the handle wafer 10 and a cap layer 40 that is bonded on top of the second device layer 30. The walls 13 of the handle wafer 10 and the frame portions 23, 33 of the first device layer 20 and the second device layer 30 together with the insulator layers 15, 25 form the walls of the enclosure.

[0042] In the illustrated example, the cap layer 40 includes a metallized contact 41 on its bottom surface that mechanically and electrically couples the support structure 32. Optionally, a metallized pattern may also be provided on the bottom surface of the cap layer 40 to act as a stationary electrode 42. The metallized contact 41 and the stationary electrode 42 are electrically coupled through the cap layer 40 to a metallized contact pad 43 on the top surface of the cap layer 40. If electrical contact is not required between the support structure 32 and the cap layer 40, the support structure 32 may be mechanically bonded to the cap layer 40 by anodic bonding. For maximum stress robustness, only the first device layer 10 should be used for the stationary electrode 21, and the cap layer 40 should not be used. Implementing an additional stationary electrode 42 on the cap layer 40 makes the MEMS device more susceptible to stress.

[0043] Optionally, the cap layer 40 may be provided with one or more bumps 44 that prevent the seismic mass(es) 31 from coming into direct contact with the stationary electrode 42 or other metallization pattern on the bottom surface of the cap layer 40. The bumps 44 are preferably made from an electrically insulating material such as SiO2 or Si4N4.

[0044] 2 shows a cross section of a MEMS device according to a second embodiment. The drawing is not to scale.

[0045] The device layer in the second embodiment corresponds to that of the first embodiment. The main difference is that a structural element 22, such as an electrode or another seismic mass, is provided in the first device layer 20 below the seismic mass 31′ for capacitive detection of the seismic mass 31′'s movement. In this case, the lateral area of ​​the structural element 22 may need to be large enough that the manufacturing method step for removing the sacrificial silicon oxide by etching does not completely remove the sacrificial insulator layer 15 between the seismic mass 31′ and the structural element 22. Perforating the seismic mass 31′ facilitates efficient removal of the sacrificial layer at the expense of reducing the mass of the seismic mass 31′. However, this may be acceptable depending on the MEMS device design.

[0046] 3 shows a cross section of a MEMS device according to a third embodiment. The drawing is not to scale.

[0047] The bottom layer 10 and second device layer 30 are similar to those in the second embodiment. Both the layout and thickness of the second layer can be designed to achieve a desired mass of the structural elements 21, 22 in the first device layer 20. Increasing mass is particularly beneficial in the vibrating elements. As will be appreciated by those skilled in the art, any of the designs described herein, including the first and third embodiments, may have structural elements, particularly the vibrating elements, in the first device layer 20 that benefit from having more mass by increasing the thickness of the first device layer 20.

[0048] 4 shows a cross section of a MEMS device according to a fourth embodiment. The drawing is not to scale.

[0049] 4, the bottom layer 10, the first device layer 20, and the second device layer 30 are according to the second embodiment, but this embodiment is equally applicable to the first and third embodiments. The main difference from any of the above-mentioned embodiments is the presence of an additional metal bonding layer 35 between the second device layer 30 and the cap layer 40. As a result, the metal bonding layer 35 introduces additional distance between the second device layer 30, and in particular the seismic mass 31 therein, and the cap layer 40, so that the second device layer does not need to be recessed on the side of the cap layer 40 during the manufacturing process. The recessing concept will be further explained below in connection with an exemplary manufacturing method.

[0050] 5a-5j illustrate an exemplary method for fabricating a MEMS device according to a first embodiment. While the process is illustrated in relation to the first embodiment, it can be easily adapted as needed to enable fabrication of devices according to other embodiments.

[0051] 5a shows a device wafer 430 that will eventually become the second device layer. The device wafer 430 is a mono-Si wafer. An electrically insulating layer 25, preferably silicon dioxide, is built on one side of the device wafer 430. Optionally, the other side of the device wafer 430 is also first protected by an electrically insulating layer 525. The electrically insulating layers 25, 525 are typically produced on the surface of the wafer using thermal oxidation, which produces an oxide layer (silicon dioxide layer) on all sides of the device wafer 430.

[0052] 5b shows the patterning of the electrical insulating layer 25. The electrical insulating layer 25 is patterned by etching. Examples of applicable etching methods are, for example, wet etching with buffered hydrofluoric acid (BHF) and reactive ion plasma etching. In this example, etching is used to remove portions 26 of the electrical insulating layer 25 in order to create poly-Si feedthroughs further in the process to electrically connect the second device layer to the first device layer.

[0053] When using wet etching, the electrically insulating layer 525 is preferably removed from the backside of the first device wafer 430 because leaving the electrically insulating layer 525 would require additional backside protection by photoresist. The net stress of the poly-Si layer needs to be low, and in some cases, preferentially tensile. Because thermally grown silicon dioxide has compressive stress, removing the electrically insulating layer 525 reduces the net stress on the top surface of the wafer in such cases, which helps minimize wafer curvature for easier handling during processing.

[0054] 5c shows the next step in which a first device layer 20 is deposited on top of the patterned electrical insulating layer 25. The first device layer 20 is a poly-Si layer. During this deposition step, a poly-Si plug 28 is created to electrically connect the first and second device layers.

[0055] Typical steps for depositing a poly-Si layer include:

[0056] 1) Depositing a thin in-situ doped poly-Si layer, which is typically performed by a low-pressure chemical vapor deposition (LPCVD) process.

[0057] 2) Depositing a thick in-situ doped poly-Si layer, which is typically performed by atmospheric pressure chemical vapor deposition (APCVD) using an epitaxial silicon deposition tool, also known as "epi-poly."

[0058] 3) Polishing the poly-Si layer using chemical mechanical polishing (CMP).

[0059] In some cases, grinding of the poly-Si layer may be necessary before it can be polished by CMP.

[0060] Steps 1 and 2 can be combined using LPCVD, but because LPCVD has a deposition rate 100–1000 times lower than APCVD, it is impractical to deposit layers with the thickness required for functional MEMS device layers. For example, the thickness of the poly-Si layer deposited in steps 1 and 2 may be on the order of 5 μm.

[0061] An alternative doping method is undoped deposition and doping of the poly-Si layer by ion implantation or diffusion from a solid source such as a doped oxide, followed by annealing.

[0062] During LPCVD, deposition of poly-Si on the backside of device wafer 430 can occur, but this can be ignored because the backside of device wafer 430 is ground later in the process to remove any unwanted deposition thereon.

[0063] The net stress in the poly-Si layer must be small.

[0064] 5d shows patterning of the first device layer 20. The first device layer is preferably patterned using lithography and etching, such as DRIE etching. During patterning, structural elements 21, 24 are formed in the first device layer 20 by a plurality of trenches that extend through the first device layer 20 to the second electrically insulating layer 25.

[0065] Figure 5e shows the stage after fusion bonding of the first element layer 20 with the handle layer 10 comprising at least one oxidation cavity 11'. For this purpose, the workpiece is flipped upside down so that the first element layer 20 is facing downwards and the second device wafer 430 is on top.

[0066] 5f shows the next step after the second device wafer 430 has been thinned to at least approximately the thickness of the second device layer 30, for example, by using grinding and / or etching. Chemical-mechanical polishing (CMP) is used to provide a smooth surface and remove any post-thinning roughness and residual surface damage from grinding. A thicker second device layer 30 facilitates a heavier, and therefore more sensitive, vibrating mass.

[0067] FIG. 5g shows a recess 330 on the top surface of the second device layer 30. The recess 330 can be formed using a local oxidation of silicon (LOCOS) process, in which SiO2 is formed in selected areas on the top surface of the second device layer 30, followed by etching to form the recess 330 on the surface. Other alternatives exist, such as etching. One purpose of the recess is to create free space above the seismic mass so that it has room for movement in the z-axis direction after the cap layer is placed on top. Instead of the LOCOS process, silicon wet etching or plasma etching can be used to create the recess. As described above with reference to the fourth embodiment shown in FIG. 4, if a metal bond is used to attach the cap layer, the creation of the recess 330 can be omitted because the metal bond layer increases the distance between the seismic mass and the cap layer, helping to avoid mechanical contact between them.

[0068] 5h illustrates the formation of structural elements, such as support structures 32 and seismic masses 31a, 31b, in second device layer 30 by patterning and etching the mono-Si layer using a dry etch such as DRIE. The structural elements in the second device layer are defined by a plurality of trenches that extend through first device layer 20 to second electrically insulating layer 25. Although not shown, the support structures in the second device layer also include springs and / or beams that control the movement of the seismic masses. During the DRIE etch, portions of second device layer 30 that are not etched are protected by a masking pattern of, for example, silicon dioxide (not shown).

[0069] FIG. 5i shows the result of releasing the structural elements in the first and second device layers 20 and 30 by removing the embedded SiO2. This can be done using hydrofluoric acid (HF) etching. In a controlled HF release, a defined amount of SiO2 is removed in all directions. The HF release also removes the electrically insulating layer from the cavity 11, removing portions of the electrically insulating layer on the suspension structure 12 and on the sidewalls 13 between the handle layer 10 and the first device layer 20, between the support structure 32 and the structural elements on the first device layer 20, and between the frame portions 23, 33 of the first and second device layers 20 and 10. Sufficient areas of the electrically insulating layers 15, 25 remain to maintain contact between the handle layer 10, the first device layer 20, and the second device layer 30, as needed.

[0070] According to some embodiments, one or more support structures 32 may be designed to have smaller lateral dimensions so that the electrically insulating layer 25 is completely removed between one or more support structures 32 and the first device layer 20. An example of a laterally small mechanical connection 38 between the first device layer 20 and the second device layer 30 is shown in FIG. 5i. Removal of the entire portion of the electrically insulating layer 25 between a structural element of the first device layer 20 and a structural element of the second device layer 30 is possible by designing at least one of the respective structural elements to have a small lateral area. In this non-limiting example, a structural element 37 in the second device layer 30 has a small lateral dimension so that all electrically insulating material is removed at this location during etching of the electrically insulating layer 25. In this way, the mechanical connection between any structural element in the second device layer 30 and a structural element in the first device layer 20 can have a distinctly smaller lateral area, facilitating smaller sizes of devices with multiple anchors. This mechanical connection is based on poly-Si and can also provide an electrical connection between the two structural elements.

[0071] Figure 5 j 1 shows the MEMS device 100 after the structural elements have been encapsulated in an enclosure by securing a cap layer 40 onto the second element layer 30. In this example, the cap layer 40 comprises glass 46, insulating silicon, and metallized contacts 41, 43, and an optional stationary electrode 42, and the cap layer 40 is attached using anodic bonding and subsequent back-end processing. Instead of a glass-insulating silicon cap layer, any other suitable type of cap layer can be used in any of the disclosed embodiments. For example, the cap layer can be an integrated circuit (IC) wafer with electrodes.

[0072] According to some embodiments, the cap layer 40 may be bonded onto the second device layer 30 using metallurgical bonding, as shown in Figure 4. In such cases, the recessing step shown in Figure 5g may be omitted such that in step 5f, the first device layer 30 is simply thinned to its desired thickness before patterning and etching to form structural elements therein.

[0073] 6a-6c illustrate the creation of stop structures, often referred to as "bumps," extending from the first device layer 20. Such stop structures may be beneficial between the first device layer 20 and the second device layer 30 to avoid attachment of the vibrating element to an overlying structure, such as an electrode or even another vibrating element. For simplicity, only some of the various material layers and structures of the MEMS device are shown.

[0074] 6a illustrates the patterning of electrical insulating layer 25 as in FIG. 5b. In addition to removing portions 26 to expose device wafer 430 to create the feedthroughs, one or more shallow recesses 626 are created in electrical insulating layer 25. These recesses 626 extend only partially through the thickness of electrical insulating layer 25.

[0075] FIG. 6b shows the first device layer 20 being deposited, simultaneously creating the feedthrough 28 and stopper structure 628.

[0076] Figure 6c shows what a typical feedthrough 28 and stopper structure 628 might look like after releasing the structural elements as shown in Figure 5i. In this simplified view, neither the first device layer 20 nor the second device layer 30 are shown with any other structural elements, but as will be understood by those skilled in the art, this is the case as shown in Figure 5i, and the bottom layer 10 is also already included in the workpiece at this stage.

[0077] It is obvious to those skilled in the art that with the advancement of technology, the basic idea of ​​the present invention can be implemented in various ways. Therefore, the present invention and its embodiments are not limited to the above examples, but may vary in various ways within the scope of the claims.

Claims

1. A MEMS (microelectromechanical systems) device, comprising, from bottom to top: a handle layer comprising at least one cavity and at least one suspension structure; a first electrically insulating layer; a first device layer formed by patterning a layer of deposited polycrystalline silicon (poly-Si), wherein at least one structural element in the first device layer is suspended by the at least one suspension structure, the at least one structural element optionally comprising at least one vibrating element; a second electrically insulating layer; and a second device layer comprising at least one vibrating element movably suspended above the first device layer, the second device layer being formed by patterning a layer of single crystal silicon (mono-Si); a cap layer bonded onto the second device layer; a first electrically insulating layer joining the handle layer and the first element layer and a second electrically insulating layer joining the first element layer and the second element layer, the first electrically insulating layer joining the handle layer and the first element layer and the second element layer being configured to form walls of a housing comprising the at least one vibration element in the second element layer, at least one stationary electrode, and at least one movable electrode for detecting and / or causing movement of the at least one vibration element, the at least one stationary electrode being in the first element layer;

2. 2. The MEMS device of claim 1, wherein the second electrically insulating layer is provided with at least one polycrystalline silicon (poly-Si) feedthrough extending from the first element layer through the second electrically insulating layer to the second element layer above the second electrically insulating layer for electrically coupling structural elements of the first element layer to structural elements of the second element layer and / or to electrical connections provided in the cap layer.

3. a plurality of the poly-Si feedthroughs extending from the first device layer to the second device layer; the electrically insulating material in the second electrically insulating layer is removed around at least one poly-Si feedthrough of the plurality of poly-Si feedthroughs; 3. The MEMS device of claim 2, wherein the at least one poly-Si feedthrough provides the only mechanical contact between the structural elements of each of the first and second device layers at each location where the electrically insulating material has been removed.

4. 4. The MEMS device according to claim 1, wherein the first element layer comprises at least one stopper structure extending toward the second element layer over a distance smaller than the thickness of the second electrically insulating layer.

5. The MEMS device of any one of claims 1 to 3, further comprising a metal bonding layer between the second element layer and the cap layer, the metal bonding layer being further configured to form part of the wall of the housing.

6. A method for manufacturing a MEMS device according to any one of claims 1 to 3, comprising the steps of: forming the handle layer from a mono-Si handle wafer, the step of forming the handle layer including forming at least one cavity and simultaneously forming the at least one suspension structure on a first surface of the handle layer and covering the first surface of the handle layer with a first electrically insulating layer; forming a second electrically insulating layer on the mono-Si wafer; patterning the second electrically insulating layer; depositing a poly-Si layer over the patterned second electrically insulating layer; forming the first device layer from the poly-Si layer, the forming the first device layer comprising thinning the poly-Si layer to a first thickness and forming a plurality of first trenches extending through the first device layer by dry etching; fusion bonding the first element layer onto the first electrically insulating layer on the first surface of the handle layer; forming the second device layer from the mono-Si wafer, the forming of the second device layer comprising thinning the mono-Si wafer to a second thickness, optionally forming at least one recessed region in the mono-Si wafer, and dry etching a plurality of second trenches extending through the mono-Si wafer; releasing structural elements of the first and second device layers by removing exposed portions of the first and second electrically insulating layers through a thickness of the first and second electrically insulating layers with a hydrofluoric acid (HF) etch; bonding the cap layer onto the second device layer, thereby encapsulating a structural element within the housing; A method comprising:

7. the step of patterning the second electrically insulating layer includes removing one or more portions of the second electrically insulating layer throughout a thickness of the second electrically insulating layer; The step of depositing a poly-Si layer includes filling the removed portions of the second electrically insulating layer with deposited poly-Si, thereby forming one or more p-type polysilicon layers extending from the first device layer through the second electrically insulating layer to the second device layer to electrically couple one or more structural elements of the first device layer and the second device layer. The method of claim 6, wherein the method produces a poly-Si feedthrough.

8. the step of patterning the second electrically insulating layer includes recessing one or more portions of the second electrically insulating layer over a portion of a thickness of the second electrically insulating layer; 7. The method of claim 6, wherein the step of depositing a poly-Si layer further comprises filling the recessed portion or portions of the second electrically insulating layer to create one or more poly-Si stop structures extending toward the second device layer.

9. 7. The method of claim 6, further comprising forming at least one recessed region in the mono-Si wafer after thinning the poly-Si layer to a first thickness and before forming a plurality of first trenches extending through the first device layer.

10. 1. The method for manufacturing the MEMS device, further comprising: a metal bonding layer between the second element layer and the cap layer, the metal bonding layer being further configured to form a portion of the wall of the housing, the method comprising: The method of claim 6 , further comprising coupling the second device layer to the cap layer by a metal bonding layer.

Images