Method for producing a microelectromechanical device, and microelectromechanical device

Abstract

The invention relates to a method for producing a microelectromechanical device (1) comprising a functional unit (2), at least one cavity (3), and a cap structure (4) that delimits the at least one cavity (3) and has at least one cavity access channel (5), wherein the at least one cavity (3) is provided between the cap structure (4) and the functional unit (2), wherein the cap structure (4) is produced by sequentially depositing and optionally structuring material layers (A1, A2, A3, M1, M2, M3, O1) on a cap substrate (6), the functional unit (2) is attached to the cap structure (4), and the at least one cavity access channel (5) is formed in the cap structure (4) by means of etching, wherein, during the production of the cap structure (4), an etch-stop structure (7) is created that covers the exit of the cavity access channel (5), projects into the cavity (3), and has an etch-stop element (8) and a first etch-stop region (9) arranged in the etch-stop element (8). The invention also relates to a micromechanical device (1).

Description

[0001] Description

[0002] title

[0003] Method for producing a microelectromechanical device and microelectromechanical device

[0004] The invention relates to a method for producing a microelectromechanical device and a microelectromechanical device.

[0005] State of the art

[0006] Microelectromechanical devices, also called MEMS devices, and methods for their manufacture are known from the prior art.

[0007] US 10626008 B2 discloses a microelectromechanical device and a method for its manufacture. The device is formed from semiconductor material and has a sensor region with multiple cavities. A cap wafer with a cavity access covers the sensor region.

[0008] US 10 508 029 B2 describes a MEMS pressure sensor and a method for its manufacture. A cap wafer is placed on the pressure sensor by eutectic bonding, with at least one cavity being formed between the pressure sensor and the cap wafer.

[0009] US 10 023461 B2 relates to a MEMS sensor comprising a sensor layer, a cap layer, and an insulation layer extending between edge regions of the sensor layer and the cap layer. A fluid path is formed by means of an air gap, a through-channel in the central region of the sensor layer, and through-openings in the cap layer.

[0010] Disclosure of the invention According to the features of independent claim 1, a method is proposed for producing a microelectromechanical device having a functional unit, at least one cavity and a cap structure delimiting the at least one cavity and having at least one cavity access channel, wherein the at least one cavity is provided between the cap structure and the functional unit, wherein the cap structure is produced by stepwise application and optional structuring of material layers on a cap substrate, the functional unit is connected to the cap structure and the at least one cavity access channel is introduced into the cap structure by etching, wherein during the production of the cap structure an etch stop structure covering an exit of the cavity access channel and protruding into the cavity is produced, said etch stop structure having an etch stop element and a first etch stop region arranged in the etch stop element.

[0011] By creating an etch stop structure that covers the cavity access channel and is adjacent to the cavity access channel exit, the functional unit of the microelectromechanical device is protected from potentially unwanted etching during the introduction of the cavity access channel into the cap substrate. The first etch stop region reliably limits the etching depth during the creation of the cavity access channel, and the cavity access channel is introduced into the cap structure only up to the first etch stop region in the etch stop structure, preventing the cavity access channel from passing straight through into the cavity, thus allowing the functional unit to be created while protecting it from etching.The etch stop structure, which covers the exit of the cavern access channel and extends into the cavern, thus allowing at least partial flow around a gas volume in the cavern on all sides, provides the etch stop region only locally in the area of ​​the cavern access channel, so that the cavern volume and a flow path between the cavern access channel and the cavern are barely affected by the etch stop structure. The manufactured etch stop structure thus provides etch protection for the functional unit and enables the implementation of low flow resistance for a gas volume flowing through the device and the implementation of a low pressure drop across the cavern access.In addition, as will be explained later, the etch stop structure can form a defined access between the cavity access channel and the cavity and thus enable additional protection of the cavity against environmental influences, liquids and / or solids above a certain, definable, particle size during operation of the device.

[0012] The etch stop element can optionally be designed at a distance from the cap substrate and can be mechanically and / or electrically connected directly to a lateral cavity boundary of the cavity and / or via at least one fastening element to the cap substrate.

[0013] Microelectromechanical devices can, in particular, be semiconductor-produced devices with microstructures that have, for example, mechanical, optical, physical, and / or chemical components and / or functions and can be used, for example, as miniaturized sensors or actuators. The microelectromechanical device can, for example, be an environmental sensor, such as a pressure sensor. A microelectromechanical device designed as a pressure sensor can be based on different pressure measurement principles, for example, as a piezoresistive or piezoelectric pressure sensor or even as a capacitive pressure sensor. However, the devices and methods described in the present application can, in principle, also be applicable to other MEMS devices, for example, designed as actuator devices.

[0014] The functional unit of the microelectromechanical device can form a functional part of the device and can be designed, for example, as a sensor unit with a sensing region. The functional unit can, for example, have one or more movable microstructures in the sensing region that are configured to perform the sensor function of the functional unit. The movable microstructure can, for example, be designed as a membrane. The functional unit can also be or have an electronic circuit or be connected to a circuit unit. The circuit and / or the circuit unit can, for example, be designed as an ASIC.

[0015] The cavity of the microelectromechanical device can be a hollow space formed between the cap structure and the functional unit, which can extend into the cap structure and, for example, enables the mobility of a microstructure of the sensing region in the cavity. The cavity can be a hollow space bounded on one side by the cap substrate or by a material layer on the cap substrate. The cavity can be bounded on its lateral sides by lateral cavity boundaries of the cap structure, which extend substantially orthogonally to the cap substrate surface. After connecting the cap substrate to a functional unit, the cavity can additionally be bounded by a surface of the functional unit.The cavity and the cavity access channel enable interaction between the microstructure and the environment of the microelectromechanical device, for example, to detect ambient pressure. The microelectromechanical device can optionally have additional cavities, such as hermetically sealed cavities with a predefined reference pressure, to enable measurements using reference-based measurement principles.

[0016] The cap structure of the microelectromechanical device can form a microstructurally produced protective covering of the functional unit, which, for example, protects a sensing region of the functional unit from mechanical impacts or undesirable environmental influences, and enables a controlled and limited interaction of the sensing region with the environment via a defined cavity access channel. The cap structure is created step by step by applying material layers to a flat cap substrate, wherein the material layers can essentially have layer planes with a larger areal extension parallel to the cap substrate surface than an extension across the layer height. The material layers can be structured in individual manufacturing steps to create specific functional cap regions and / or prepare for further manufacturing steps.For example, limited areas or sections of the material layers can be removed locally, for example by applying a mask to the material layer and / or the material layers and subsequent etching.

[0017] The cavity access channel introduced into the cap structure can, for example, be generated substantially orthogonally to the cap substrate surface. The cavity access channel can be formed so as to completely penetrate the cap substrate. The cavity access channel has an exit facing the cavity and an entrance facing away from the cavity. The etch stop structure can be provided covering the exit of the cavity access channel. The etch stop structure can be formed adjacent to the exit of the cavity access channel. "Adjacent" can mean that a structure or component of the etch stop structure in the region of the cavity access channel, in particular in the region of the exit of the cavity access channel facing the cavity, is directly connected to the cap substrate or is provided at a distance from the cap substrate.The formation of a fluid path between the cavity access channel and the cavity can be achieved, for example, by providing at least one etch stop element, at least one fastening element, and / or at least one connecting channel in the region of the etch stop structure and / or the cap substrate. It is also conceivable for the etch stop structure to adjoin a region adjacent to the cavity access channel on the cavity side, i.e., in other words, for the etch stop structure to be connected, for example, to the cap substrate in such a way that the central axis of the etch stop structure is offset from the central axis of the cavity access channel. Such an offset can, for example, be smaller than the smallest lateral dimension of the etch stop structure, for example, also smaller than the smallest lateral dimension of a fastening element of the etch stop structure. The cavity access channel can be used for area optimization of a MEMS device, e.g.a sensor and / or actuator device, can be arranged in the cap structure above a sensing region of the functional unit. The cavity access channel can, for example, be introduced into the surface of the cap structure essentially centrally or at least in a region close to the center of the sensing region. This can, for example, enable a subsequent molding process, such as film-assisted molding (FAM), of the microelectromechanical device, in which the device is provided with a housing consisting of a robust encapsulation material outside the at least one cavity access channel for improved protection.In this case, the process requires sealing of the cavern access channel on the side of the cap substrate facing away from the cavern. This, in turn, requires a sufficient covering surface surrounding the cavern access channel for attaching a protective film, so that a location of the cavern access channel close to the center of the sensing area can be advantageously implemented. In principle, multiple cavern access channels can also be created and / or the at least one cavern access channel can be located outside of a sensing area close to the center, e.g., in the area of ​​a lateral cavern boundary.

[0018] The etch stop structure of the cap structure can be formed by applying material layers and structuring them on a component of the cap structure, for example, on the cap substrate. The etch stop structure has an etch stop element that forms a support structure for the first etch stop region and that protects the first etch stop region from etching attack in a sacrificial layer etching process. The etch stop element can be made, for example, from a silicon material, for example, polysilicon. The etch stop structure is created such that it protrudes into the cavity provided between the cap structure and a later-connected functional unit. The etch stop structure can therefore be surrounded at least partially on its circumference by the cavity cavity and / or a gas volume accommodated therein.Furthermore, the etch stop structure can, for example, also be connected to and / or integrated into a lateral cavity boundary at least on one side and at least partially.

[0019] The first etch stop region can be a material layer or a structured region of a material layer that preferably has a higher etch selectivity or etch resistance to an etching process forming a cavern access channel and the etching media used therein than material layers at least directly adjacent to the first etch stop region and can prevent an etching process or etching progress into material layers protected by the etch stop region. For example, the material layer of the first etch stop region can be chemically and / or physically more resistant than at least directly adjacent layers and / or have a significantly lower etch rate than at least directly adjacent layers. The etch stop region is advantageously matched to the etching processes and etching media used to produce the cap structure and / or a cavern access channel.

[0020] The application of material layers, which can in particular be semiconductor-based material layers such as monocrystalline or polycrystalline silicon layers or dielectric layers made of silicon compounds such as silicon dioxide (SiCh) or silicon nitride (SiS1^), can be carried out, for example, by deposition using deposition methods known in semiconductor technology. The material layers are applied to a cap substrate, also called a cap wafer, whereby the cap substrate can be a silicon substrate, for example. A material layer can be applied continuously or in regions on the substrate and / or on an already applied material layer. The structuring and / or the introduction of cavities and / or depressions is possible, for example, using etching processes, whereby local removal of layer material is possible, for example, by masking.The etching processes can advantageously be carried out using dry etching methods, such as plasma etching. However, wet-chemical etching processes are also generally usable. Furthermore, the device can be processed using other processing methods in additional optional manufacturing steps, for example, by thinning it using a grinding process and / or chemical-mechanical polishing (CMP process).

[0021] The functional unit can be connected to the cap structure, for example, in a bonding region by means of a bonding frame structure and, for example, using a wafer bonding process known in semiconductor technology. The bonding frame structure can connect the cap structure to the functional unit mechanically and / or at least partially electrically conductively and / or at least partially electrically non-conductively. The bonding frame structure can be made, for example, from a thermo-compressive material containing, for example, gold, or from a eutectic material containing, for example, aluminum, silicon, germanium, copper, and / or gold, or from a material containing tin and / or copper, or from a polymer-based material or a glass frit material.Between the bond frame structure and the cap structure, at least one dielectric layer, which contains, for example, silicon (Si), aluminum (Al), titanium (Ti), tantalum (Ta), oxygen (O) and / or nitrogen (N), and / or at least one adhesion-enhancing layer, which contains, for example, tantalum (Ta), titanium (Ti), tungsten (W), nickel (Ni), nitrogen (N) and / or platinum (Pt), or a layer combination of layers with the aforementioned materials can be provided, which can optionally also be used to produce electrical conductor tracks and electrical contact structures.The aforementioned chemical elements can also be present as chemical compounds in the layers, for example as silicon dioxide (SiO2), silicon nitride (SiN4), silicon oxynitride (SiON), titanium oxide (TiO2), tantalum oxide (Ta2Os) and / or aluminum oxide (Al2O3) in a dielectric layer or, for example, as tantalum nitride (TaN), titanium nitride (TiN) and / or titanium tungsten (TiW) in an adhesion-enhancing layer.

[0022] The functional unit can, for example, be provided on a separate functional wafer and connected to the cap structure provided on another wafer, here on the cap substrate, using a wafer bonding process. The microelectromechanical device can thus, for example, comprise a cap wafer and a functional wafer connected thereto.In the lateral direction, i.e., viewed parallel to the substrate surfaces, for example, the microelectromechanical device can have, for example, a bonding region provided for the mechanical and / or electrical connection of the functional unit to the cap structure, an adjoining sensing region of the functional unit, in which the device is configured to perform a sensor function by means of at least one microstructure, and a bonding pad region in which electrical contact can be made with the sensing region via electrical conductor tracks and by means of wire bond connections to, for example, an evaluation circuit. According to one embodiment, the first etch stop region can be enclosed in the etch stop element in such a way that it is, in particular, completely surrounded by the etch stop element.This makes it possible to protect the first etch stop region from etching attack during etching process steps that take place prior to the introduction of the cavity access channel. The first etch stop region can form a buried hard mask. The enclosure can be achieved, for example, by applying and structuring an etch stop layer on a first material layer of the etch stop element and by covering the etch stop layer with a second material layer of the etch stop element, wherein the second material layer can cover the first etch stop region such that it is also laterally surrounded by the second material layer. The first and second material layers of the etch stop element can be made of a silicon material, for example, polysilicon.

[0023] According to one embodiment, at least one connecting channel connecting the cavity to the cavity access channel is created between the etch stop element and the cap substrate and / or in the etch stop element and / or in the cap substrate. This allows a fluid path to be formed between the cavity access channel and the cavity and to be configured according to individual requirements for the cap structure or the device. For example, a connecting channel between the etch stop element and the cap substrate can be created by applying and subsequently removing a sacrificial material layer. The height of the sacrificial material layer can be used to define the height of the subsequent connecting channel. The height of the connecting channel and its other lateral dimensions can be used to establish a barrier effect for particles or liquids above a certain particle size.The production of at least one connecting channel in the cap substrate can be achieved, for example, by etching a blind-hole-shaped depression into the substrate surface. This enables simple production of the connecting channel by machining the cap substrate before applying further material layers to the cap substrate. A connecting channel produced in the cap substrate can advantageously also form an etching channel through which an etching medium can be introduced into the cap structure, so that an etching process can be simplified or accelerated. One connecting channel can form a lateral channel that runs essentially orthogonal to the perpendicular bisector of the cavity access channel and opens into this and into the cavity. Multiple connecting channels can form lateral channels that run essentially orthogonal to the perpendicular bisector of the cavity access channel and open into this and into the cavity.The etch stop structure can at least partially cover one lateral channel produced in the cap substrate or several lateral channels produced in the cap substrate. If the etch stop structure does not completely cover the lateral channel or the lateral channels produced in the cap substrate, a fluid in the uncovered area can enter or exit the lateral channel or the lateral channels. If the etch stop structure completely covers the lateral channel or the lateral channels produced in the cap substrate, at least one exit channel can be introduced into the etch stop structure to create a fluid path between the cavity and a lateral channel. An exit channel in the etch stop structure can extend laterally offset from the cavity access channel.The output channel may extend substantially orthogonally to the adjoining lateral channel.

[0024] In principle, it is conceivable to produce at least one connecting channel in the etch stop structure and additionally at least one connecting channel in the cap substrate. Furthermore, it may be advantageous to fluidically connect connecting channels to one another in order to further reduce flow resistance. The geometric dimensions and / or shapes of the cavity access channel, the lateral connecting channel, and / or the exit channel running substantially perpendicular to the lateral connecting channel can be selected such that only gaseous media can flow through the cavity access, while liquids or solid particles above a certain particle size are prevented from entering the cavity. This can be further promoted by diverting the cavity access channel into the connecting channel and, if necessary, by further diverting it into an exit channel.According to one embodiment, the first etch stop region can be provided by means of the etch stop element and / or by means of a fastening element by fastening it to the cap substrate and / or to a lateral cavity boundary at a distance from the exit of the cavity access channel. In this case, the first etch stop region can, in particular, cover the exit of the cavity access channel. The etch stop structure can therefore be produced, for example, by applying material layers such that the etch stop element with the first etch stop region provided therein does not directly adjoin the cavity access channel, in particular not directly adjoin an exit of the cavity access channel, or in other words, at least one further material layer is introduced between the cavity access channel and the etch stop element surrounding the etch stop region. The further material layer can, for example, be a sacrificial material layer.The further material layer can correspond to the material layer of the etch stop region. By spacing the etch stop element with the first etch stop region provided therein from the cavity access channel, for example, the creation of a connecting channel between the cavity and the cavity access channel can be enabled and / or the introduction of the cavity access channel can be better controlled. Furthermore, the first etch stop region can be protected from etching attack by providing a surrounding etch stop element during etching process steps that take place prior to the introduction of the cavity access channel, for example, during the removal of the further material layer.

[0025] According to one embodiment, the first material layer or the first etch stop region of the etch stop element can directly adjoin the exit of the at least one cavity access channel. This allows for the realization of a compact etch stop structure. The etch stop element and / or the etch stop region can, in particular, completely cover the exit of the cavity access channel.

[0026] According to one embodiment, at least one

[0027] Access to a bond pad area and / or bond pad structures of the cap structure can be achieved. This allows good accessibility to the bond pad area and / or the bond pad structures.

[0028] According to one embodiment, the etch stop element can be connected to the cap structure and / or to a lateral cavity boundary by means of at least one fastening element. For example, the etch stop element can be connected to the cap substrate by means of the fastening element. The fastening element can be formed outside the cavity access channel so that it can be held on a structure surrounding the cavity access channel. The fastening element can be an integral part of the etch stop element. The fastening element can be made of the same material as the etch stop element, for example, from a silicon material comprising silicon or a silicon compound.The fastening element can be formed over the entire surface between the etch stop element and the cap substrate, or it can form a substantially point-like or section-wise coupling of the etch stop element to the cap substrate and / or to a lateral cavity boundary, allowing the etch stop element to be spaced apart from the cap substrate. The fastening element can, for example, be substantially cuboid- or cube-shaped, web-shaped, ring-shaped, ring-segment-shaped, or have another suitable geometric shape. The etch stop element can be connected to the cap substrate by means of multiple fastening elements.

[0029] For example, several cuboid- or web-shaped fastening elements can form a lattice structure via which the etch stop element is connected to the cap substrate. An etch stop element spaced apart from the cap substrate can form at least one fluid path between the cavity and the cavity access channel. In other words, at least one connecting channel can be formed in the etch stop structure in the plane of the fastening element. Such a connecting channel can be created, for example, by a sacrificial material layer that is applied and subsequently removed, whereby the distance between the etch stop element and the cap substrate, the height of a fastening element, and the height of the connecting channel can be defined via the thickness of the sacrificial material layer.The geometric dimensions with regard to length and cross-section and / or the shape of the at least one connecting channel can be selected such that only gaseous media can flow into the cavern, while liquids or solid particles above a certain particle size are prevented from entering the cavern.

[0030] According to one embodiment, to produce the fastening element, a sacrificial material layer can be applied and then removed again in certain regions, wherein at least one region in which sacrificial material was removed is at least partially filled by a material layer applied to the sacrificial material layer. This allows the fastening element to be produced in a simple manner. The filled region or regions can each form a fastening element that connects the etch stop element to the cap substrate. The further material layer can in particular be a material layer of the etch stop element and, for example, made of a silicon material, for example polysilicon. The sacrificial material layer can, for example, be a silicon dioxide layer. The sacrificial material layer can, for example, be applied to the cap substrate and structured, such that the fastening element can be produced on the cap substrate.The sacrificial material layer can optionally also be created using multiple individual sacrificial material layers. The sacrificial material layer can optionally also be maintained and / or structured outside the etch stop element to prepare for further process steps and / or to be part of the layer system surrounding the cavity.

[0031] The first etch stop region can be formed, for example, from silicon dioxide. This creates an etch stop region that is easy to manufacture yet highly effective. The first etch stop region made of silicon dioxide can, for example, exhibit high chemical etch resistance in a plasma etching process, allowing the cavity access channel to be introduced in a controlled manner, and the insertion depth can be reliably controlled or limited by the first etch stop region.

[0032] According to one embodiment, before and / or during and / or after the

[0033] To create the cavern access channel, a cap substrate recess can be created. By providing a cap substrate recess, the entrance of the cavern access channel can be designed on the side of the cap substrate facing away from the cavern, spaced from the surface of the cap structure, thereby preventing mechanical damage and / or deposition of protective film material in the film-assisted molding (FAM) process in the region of the entrance of the cavern access channel. The creation of the cavern access channel can be preceded by re-thinning the cap substrate to a desired target thickness, for example, by grinding and / or polishing.To prepare for the production of the cavity access channel and the cap substrate recess, regions of the cap substrate on the side of the cap substrate facing away from the etch stop structure, hereinafter also referred to simply as the back of the cap substrate, can be masked with a third etch stop region or with a third etch stop layer, and a photoresist mask can then be applied to the cap structure such that no photoresist is present at least in the region of the cavity access channel. The cavity access channel can then be etched, wherein the etching process can advantageously stop at the first etch stop region of the etch stop structure. During or after etching the cavity access channel, the photoresist mask can be removed, and the cap substrate recesses can be introduced into the regions of the cap substrate not masked by the third etch stop region or the third etch stop layer.The third etch stop region or the third etch stop layer can then optionally be removed or remain on the cap structure as mechanical protection and mechanical contact area of ​​the cap structure for further process steps or for the operation of the device.

[0034] For some microelectromechanical devices, it may be desirable to create the largest possible cavity volume. In principle, it is conceivable to choose the layer thicknesses of the material layers forming the etch stop element and the lateral cavity boundaries as large as possible in order to create a large cavity.

[0035] According to one embodiment, a second etch stop region can be created on the etch stop structure, and by subsequently applying at least one further material layer, a lateral cavity boundary of the cap structure can be increased such that the height of the lateral cavity boundary of the cap structure relative to the cap substrate is greater than the height of the etch stop structure relative to the cap substrate. This allows the distance of the etch stop structure from a subsequently connected functional unit to be increased, so that potential impairment of, for example, movable microstructures of the functional unit by the etch stop structure is reliably excluded, and the freedom of movement of a movable microstructure of the functional unit can be increased, so that, for example, a greater deflection of a microstructure is possible.In addition, the increased cavity volume, for example for a microelectromechanical device designed as a sensor device, can reduce a time-dependent effect, e.g. the increase in the internal pressure of the cavity caused by the diffusion of gaseous elements through the layer system surrounding the cavity, so that the service life of the sensor device is increased. The height of the lateral cavity boundary relative to the cap substrate can be understood as the extension of the lateral cavity boundary orthogonal to a substrate surface or main extension plane of the cap substrate. The height of the etch stop structure relative to the cap substrate can be understood as the extension of the etch stop structure orthogonal to a substrate surface or main extension plane of the cap substrate. The second etch stop region can be a hard mask defining the lateral dimensions of the etch stop structure, consisting of, e.g.Silicon dioxide can be understood. During the above-described increase in the lateral cavity boundary by applying and selectively removing at least one further material layer, the etch stop structure is reliably protected by the second etch stop region, so that the function of the first etch stop region incorporated in the etch stop structure for the introduction of the cavity access channel can be reliably maintained.

[0036] According to one embodiment, a cavity recess can be introduced into the cap substrate of the cap structure during and / or after the creation of the etch stop structure. This enlarges the cavity into the cap substrate. For this purpose, the etch stop structure and the lateral cavity boundaries of the cap structure can be masked, for example, with a photoresist mask, and etching can occur down into the cap substrate. If a sacrificial material layer was applied to the cap substrate in a previous process step, this can first be removed in a preparatory step for introducing the cavity recess in the region of the cap substrate in which the cavity recess is to be created.The removal of the remaining sacrificial material layer, for example in a region between the etch stop element and the cap substrate, can take place after the cavity recess has been formed or at a later time. A cavity recess can enable an enlargement of the cavity formed between the cap structure and the functional unit, thus achieving an increase in the enclosed cavity volume. A larger cavity, for example for a microelectromechanical device designed as a sensor device, can reduce a time-dependent effect, such as the increase in the internal cavity pressure per unit time caused by the diffusion of gaseous elements through the layer system surrounding the cavity, thus increasing the service life of the sensor device.

[0037] Furthermore, it is conceivable that, during the production of the cap structure, a bond pad region recess and / or a through-opening in the region of bond pad structures are introduced into the cap structure. Providing a recess in the region of bond pad structures can be advantageously used, for example, to avoid having to remove the entire thickness of the cap structure after or during the creation of the cavern access channel in order to be able to create free access to bond pad structures and / or a bond pad region. An opening that completely penetrates the cap structure can be provided in the region of bond pad structures.

[0038] After the cavity access channel has been introduced into the cap structure, the cavity access channel can optionally be closed again, for example, by melting layer and / or substrate material using a laser and / or by depositing at least one electrically conductive and / or electrically non-conductive sealing layer. This may be desirable, for example, for sensors in microelectromechanical devices that operate with a closed cavity and a defined internal cavity pressure, such as inertial sensors.

[0039] In principle, it is conceivable that the applied silicon layers and / or the cap substrate can be doped in order to increase their electrical conductivity and thus, for example, can additionally serve as EMC shielding.

[0040] According to the features of independent claim 12, a microelectromechanical device is proposed having a functional unit, at least one cavity and a cap structure delimiting the at least one cavity with at least one cavity access channel, wherein the at least one cavity is provided between the cap structure and the functional unit, wherein the cap structure has a cap substrate and at least one material layer applied thereon and optionally structured, and wherein the cap structure has an etch stop structure covering the exit of the cavity access channel and projecting into the cavity, said etch stop structure having an etch stop element and a first etch stop region arranged in the etch stop element.

[0041] This makes it possible to provide a device that is easy and process-reliable to manufacture, the functional unit of which is advantageously protected by the etch stop structure from process influences during manufacture and also from environmental influences during operation.

[0042] According to one embodiment, the first etch stop region can, in particular, be completely surrounded by the etch stop element. This makes it possible to provide a device that is easy and reliable to manufacture, since the first etch stop region is protected from etching during the etching process steps that take place prior to the introduction of the cavity access channel.

[0043] According to one embodiment, the cap structure can have at least one connecting channel connecting the cavity to the cavity access channel between the etch stop element and the cap substrate and / or in the cap substrate. This allows a fluid path to be formed between the cavity access channel and the cavity and configured according to individual requirements for the cap structure or the device.

[0044] The device may also have further features presented in connection with the method described above, for example

[0045] - the first etch stop area must be provided covering an exit of the cavern access channel

[0046] - the first etch stop region is provided at a distance from an exit of the cavern access channel by means of the etch stop element and / or by means of a fastening element;

[0047] - the etch stop element is connected to the cap structure and / or to a lateral cavity boundary by means of at least one fastening element;

[0048] - that the first material layer and / or the first etch stop region of the etch stop element directly adjoin an exit of the cavern access channel;

[0049] - the cap structure has a cap substrate recess;

[0050] - a lateral cavity boundary of the cap structure has a greater height relative to the cap substrate than the etch stop structure;

[0051] - the cap structure has a cavernous depression and / or

[0052] - the cap structure has access to bond pad structures and / or to a bond pad area.

[0053] The device and method described above can be used, for example, in MEMS sensor technology. In principle, the method can be used to manufacture any microelectromechanical device in which a cavity with a cavity access channel is provided or required. The presented method can prevent etching on a sensing area of ​​the device, but also, in principle, on other device components such as circuit elements.

[0054] In general, in the context of this application, the words “a / an”, unless expressly defined otherwise, are not to be understood as a number, but as an indefinite article with the literal meaning of “at least one”.

[0055] The invention permits various embodiments and is explained in more detail below using exemplary embodiments with the accompanying drawings. They show:

[0056] Fig. 1-6 - based on schematic lateral sectional views

[0057] Method steps for producing a microelectromechanical device according to a first embodiment;

[0058] Fig. 7-8 - based on schematic lateral sectional views

[0059] Method steps for producing a microelectromechanical device according to a second embodiment;

[0060] Fig. 9a-9b - based on schematic lateral sectional views

[0061] Method steps for producing a microelectromechanical device according to a third embodiment;

[0062] Fig. 10 - a schematic sectional view of a

[0063] Method step for producing a microelectromechanical device according to a fourth embodiment;

[0064] Fig. 11 a-11 c - enlarged views of a section of Fig. 10 according to three

[0065] Variants of the fourth embodiment.

[0066] Reference is first made to Fig. 6 to explain a first exemplary embodiment of a microelectromechanical device 1 that can be manufactured using the method described in more detail below. Fig. 6 shows a microelectromechanical device 1 according to a first embodiment. The device 1 shown has a functional unit 2, at least one cavity 3, and a cap structure 4 delimiting the cavity 3 with at least one cavity access channel 5, wherein the at least one cavity 3 is provided between the cap structure 4 and the functional layer 2. The cap structure 4 has an etch stop structure 7 covering the exit of the at least one cavity access channel 5 and protruding into the cavity 3, said etch stop structure having an etch stop element 8 and a first etch stop region 9 arranged in the etch stop element 8.

[0067] By producing an etch stop structure 7 covering the exit of the cavity access channel 5, the functional unit 2 of the microelectromechanical device 1 is protected from unwanted etching during the introduction of the cavity access channel 5. The first etch stop region 9 reliably limits the etching depth during the production of the cavity access channel 5. By the etch stop structure 7 covering the exit of the cavity access channel 5, protruding into the cavity 3 and thus at least partially surrounded by a gas volume in the cavity, the etch stop region 9 is provided only locally in the region of the cavity access channel 5, so that the cavity volume and a flow path 10 between the cavity access channel 5 and the cavity 3 are barely affected by the etch stop structure 7. In principle, material of the etch stop region 9 can also be present in the layer system surrounding the cavity 3.In addition, the etch stop structure 7 can form a defined access between the cavern access channel 5 and the cavern 3 and thereby provide additional protection for the cavern 3 against environmental influences.

[0068] Liquids and / or solids above a certain particle size enable the operation of the device 1.

[0069] In Fig. 6, the already etched cavity access channel 5 is shown as an open space. In connection with the method steps for manufacturing the device 1 described below, the intended cavity access channel 5 is indicated by a dashed line in the process steps preceding the etching to illustrate its intended position in the cap structure 6.

[0070] The functional unit 2 of the device 1 shown in Fig. 6 can be a sensor unit, for example. The region of the cavity 3 can be understood as a sensing region 16, while a laterally adjacent region with a bond frame structure 17 and a bond pad (not shown in detail) is referred to as a bond pad region 15 and can be used for electrically contacting the device 1. The bond pad region 15 has a bond pad region recess 21. The cap substrate 6 of the cap structure 4 has an optional cap substrate recess 12 and an optional third etch stop region 18. The cavity 3 has lateral cavity boundaries 20.The etch stop structure 7 has an etch stop element 8, a first etch stop region 9 fully enclosed therein, at least one fastening element 11, and at least one connecting channel 10 formed between the etch stop element 8 and the cap substrate 6 for connecting the cavity access channel 5 to the cavity 3. The components and features described above will be explained in more detail with reference to the method steps for producing the device 1.

[0071] An exemplary embodiment of a method for producing the microelectromechanical device 1 according to the first embodiment is explained below with reference to FIGS. 1 to 6, wherein FIGS. 1 to 3 essentially show the production of the cap structure 4 and FIGS. 4 to 6 essentially show the further production of the device 1. In FIG. 1, it can be seen that a sacrificial material layer 01, for example made of silicon dioxide, was first deposited on a cap substrate 6. The sacrificial material layer 01 was structured in such a way that sacrificial material was removed in a bond frame region, shown in the drawing above bond frame structures 17.It is also conceivable to provide sacrificial material of the sacrificial material layer 01 outside the cavity region in such a way that it is not removed during a sacrificial layer etching process for removing sacrificial layer material of the sacrificial material layer 01 in the cavity region and can remain at least partially, for example in the region of bond frame structures 17. In addition, sacrificial material was removed in a region adjacent to the cavity access channel 5 in order to be able to form fastening elements 11 of the etching stop structure 7 in a subsequent step. As can be further seen from Fig. 1, after the structuring of the sacrificial material layer 01, a first material layer M1 was deposited in such a way that regions in which the sacrificial material layer 01 was removed were at least partially filled with material of the material layer M1.Thus, fastening elements 11 of the etch stop structure 7 were produced by the first material layer M1, which can be made of polysilicon, for example. The first material layer M1 also forms part of the etch stop element 8 of the etch stop structure 7. If, as indicated in Fig. 1, material of the sacrificial material layer 01 was removed at several points in areas adjacent to the cavity access channel 5 and several fastening elements 11 were formed by filling, these can, for example, form a lattice structure around the cavity access channel 5, which can later prevent particles from penetrating the cavity 3. The height of the fastening elements 11 depends on the thickness of the sacrificial material layer 01, so that the particle sizes that can be prevented from entering the cavity 3 can be defined via the spacing of fastening elements 11 and / or by selecting the layer thickness of the sacrificial material layer 01.Since, for example, a sacrificial material layer 01 made of silicon dioxide can be produced very thin, effective protection against the penetration of even very small particles can be achieved.

[0072] After deposition, the first material layer M1 can optionally be planarized to create a flat surface. As can be further seen from Fig. 1, in a further step, a first etch stop layer A1 was applied and structured in order to be able to form at least a first etch stop region 9 in the etch stop structure 7. In principle, material of the etch stop region 9 can also be present in the layer system surrounding the cavity 3. The first etch stop region 9 can, for example, be made of silicon dioxide. The first etch stop region 9 later serves as an etch stop surface for limiting the insertion depth of the cavity access channel 5, as will be described in more detail later. As can be further seen from Fig. 1, in a further step, a second material layer M2, which can, for example, be made of polysilicon, was deposited, so that the first etch stop region 9 is covered by the material layer M2, in particular also enclosed laterally.The second material layer M2 can then optionally be planarized. As can be further seen from Fig. 1, a bond frame structure 17 was created on the second material layer M2 in a further step. The bond frame structure 17 can have at least one element for producing a eutectic bond, a thermocompressive bond, or for producing a solder connection between the cap substrate 6 and a functional unit 2 and can contain, for example, the elements gold, tin, nickel, aluminum, titanium, tantalum, tungsten, copper, germanium, silicon, oxygen, or nitrogen. The bond frame structure 17 can optionally also consist of, for example, a glass frit, seal glass, or glass solder material.

[0073] In principle, it is also conceivable to construct the etching stop element 8 from the material of a second material layer M2 and / or a third material layer M3 if, before the deposition of this material layer or material layers, suitable recesses have been created in the previously applied material layers.

[0074] Fig. 2 shows that after the production of the bond frame structure 17, a first photoresist mask F1 was applied, which covers at least a region of the provided etch stop structure 7, the bond frame structure 17, and regions of the cap structure 4 that are provided for forming a lateral cavity boundary 20 and / or for forming a bond pad region recess 21. In particular, the first photoresist mask F1 was provided in the region of the provided etch stop structure 7 such that the first etch stop region 9 is located entirely within the region masked by the photoresist mask F1, and any existing fastening elements 11 are at least partially located within the region masked by the photoresist mask F1.In order to avoid unwanted etching of the first etch stop region 9 during a subsequent etching step for removing the sacrificial material layer 01, the position of the first etch stop region 9 within the region masked with the photoresist mask F1 is preferably selected such that a defined, minimum distance is not undercut between the etch stop region 9 and the peripheral contour of the masked region. As can be seen further from Fig. 2, an etching process, here for example a silicon etching process, was subsequently carried out, which removed the first material layer M1 and the second material layer M2 in regions not masked with a photoresist mask F1 and which stops on the sacrificial material layer 01 made of silicon dioxide. The etching process formed the cavity 3 with lateral cavity boundaries 20 and the etch stop structure 7. In addition, a bond pad region recess 21 was optionally formed using the same etching process.By means of a first photoresist mask F1 applied over a correspondingly large area, the etching stop structure 7 can be formed in such a way that the first etching stop region 9 in the etching stop element 8, which was produced from the first material layer M1 and the second material layer M2, is provided at a distance from the circumferential contour of the etching stop element 8.

[0075] In Fig. 3 it can be seen that the sacrificial material layer 01 was completely removed in a further step in order to expose the at least one fastening element 11 and to create a connecting channel 10 in the region of the etch stop structure 7 between the etch stop element 8 and the cap substrate 6, through which connecting channel 10 a fluid path between the cavity access channel 5 and the cavity 3 can be formed. In other words, by removing the sacrificial material layer 01 between the cap substrate 6 and the further etch stop element 8 of the etch stop structure 7, a connecting channel 10 is produced, in which a cross-sectional area of ​​the connecting channel 10 can be produced that can be defined via the distance or distances between fastening elements 11 and / or the thickness of the sacrificial material layer 01. After removing the first photoresist mask F1, a prepared cap structure 4 is now present, which can be connected to a functional unit 2 as shown in Fig. 4.

[0076] Fig. 4 shows that, in a further step, the prepared cap structure 4 can be connected to the functional unit 2 via the bond frame structure 17. The functional unit 2 can, for example, be a functional wafer with MEMS and / or ASIC components. The etch stop structure 7 can prevent an etch attack on the surface of the functional unit 2 later during the production of the cavern access channel 5. Following the connection of the functional unit 2, the cap substrate can

[0077] 6 and / or the functional unit 2 can optionally be thinned to a desired target thickness in a re-thinning step by grinding and / or polishing.

[0078] In Fig. 5, it can be seen that, in a further step, third etch stop regions 18 can be produced on a rear side of the thinned-back cap substrate 6, which third etch stop regions were produced, for example, from an applied and structured third etch stop layer A3. The third etch stop layer A3 can, for example, be a silicon dioxide layer. At this point, it should be briefly noted that a second etch stop region 13 will be explained below in connection with the second embodiment according to Fig. 7. The third etch stop regions 18 can serve, in a subsequent step, to produce a cap substrate recess 12 and / or to produce access to a bond pad region 15 and can later optionally form mechanical protection or a mechanical contact region of the device 1. Fig.It can further be seen from Fig. 5 that a second photoresist mask F2 can be applied to the third etch stop regions 18 and to the back of the cap substrate 6, wherein the region of the cavity access channel 5 was left out during the masking. It can further be seen from Fig. 5 that the cavity access channel 5 was etched through the cap substrate 6 by means of an etching process, in particular a plasma etching process, wherein the plasma etching process removed not only cap substrate material but also, at least in some regions, the first material layer M1 in the etch stop structure 7. After the at least partial removal of the first material layer M1, the plasma etching process stops on the first etch stop region 9, so that an etching attack on the functional unit 2 can be avoided.If material of the third etch stop regions 18 is optionally located in the region of a cavity access channel 5, this material must also be removed when the cavity access channel 5 is introduced through the cap substrate 6. Alternatively, the material of the third etch stop regions 18 can also be removed by performing a separate etching process before the cavity access channel 5 is introduced. As can be seen from Fig. 6, after the cavity access channel 5 was introduced through the cap substrate 6, the second photoresist mask F2 was removed in a further step, and a cap substrate recess 12 was created, wherein the third etch stop regions 18 acting as a mask can predefine a lateral boundary of a cap substrate recess 12, at least in some regions. The third etch stop regions 18 can then optionally be removed or remain on the device 1 as a mechanical contact region.

[0079] 7 and 8 in order to explain a microelectromechanical device 1 and a method for its production according to a second embodiment, wherein two individual intermediate states of the method have been selected and further steps can be carried out analogously to the method according to the first embodiment. For some microelectromechanical devices 1, it may be desirable to produce the largest possible cavity volume. In principle, it is conceivable to select the layer thicknesses of the material layers M1 and M2 forming the etch stop element 8 and the lateral cavity boundaries 20 to be as large as possible in order to be able to produce a large cavity 3. However, it is also possible, for example, as shown in Fig. 7, to produce a second etch stop region 13 on the etch stop structure 7 by applying and structuring a second etch stop layer A2 and subsequently applying at least one further material layer M3.Thereafter, regions of the cap structure 4 can be masked with a photoresist mask F1 in order to predefine the lateral cavity boundaries 20 and / or lateral boundaries of a bond pad region recess 21, and subsequently the cavity 3 and / or the bond pad region recess 21 can be etched into the cap structure 4, wherein the etching process stops on the sacrificial material layer O1. The second etch stop region 13 previously applied to the etch stop structure 7 reliably protects the etch stop structure 7 in the cavity 3 from etching attack, so that its function is retained. The third material layer M3 increases the cavity size of the cavity 3 and also increases the distance between the etch stop structure 7 and the functional unit 2, as can be seen from Fig. 8. After the cavity 3 has been produced, the second etch stop region 13 can optionally be removed together with the sacrificial material layer O1. Fig.Fig. 8 shows the device 1 in a state after the connection of the cap structure 4 to the functional unit 2 and after the introduction of a cap substrate recess 12 and the cavity access channel 5. It is also evident in Fig. 8 that the lateral cavity boundary 20, due to the elevation 20' by means of the third material layer M3, has a greater height hi relative to the cap substrate 6 than the etch stop structure 7 with a height h2. The distance of the etch stop structure 7 from the functional unit 2 can be determined via the height of the further material layer M3.

[0080] Reference is made below to Figs. 9a and 9b to explain a microelectromechanical device 1 and a method for its production according to a third embodiment, wherein two individual intermediate states of the method have been singled out and further steps can be carried out analogously to the method according to the first and / or second embodiment.

[0081] Fig. 9a shows that, after the production of the etch stop structure 7, a cavity recess 14 was introduced into the cap substrate 6 of the cap structure 4. For this purpose, sacrificial material from a sacrificial material layer 01 deposited on the cap substrate 6 was removed in the region of the intended cap recess 14 such that the remaining sacrificial material of the sacrificial material layer 01 serves, at least in some areas, as an etching mask during the production of the cap recess 14. Preferably, material of the sacrificial layer 01 remains in the region of the etch stop structure 7 between the etch stop element 8 and the cap substrate 6 for producing at least one connecting channel 10 between the cavity access channel 5 and the cap recess 14 and / or the cavity 3.A first material layer M1, a first etch stop region 9, and a second material layer M2 are subsequently provided on the structured sacrificial material layer 01, and optionally a second etch stop region 13 and a third material layer M3 are provided to produce an etch stop structure 7. Subsequently, the region of the etch stop structure 7 and regions of the cap structure 4 were masked with a photoresist mask F1, and etching was performed down into the cap substrate 6. The cavity recess 14 allows the cavity volume of the cavity 3 to be increased in the direction of the cap substrate 6, so that a more compact device 1 with a large cavity volume can be provided. Fig. 9b shows that the remaining sacrificial material layer 01 between the etch stop element 8 of the etch stop structure 7 and the cap substrate 6 was subsequently removed, and the cap structure 4 is prepared for connection to the functional unit 2.In this exemplary embodiment, the sacrificial material layer 01, which additionally serves as an etching mask, is provided in the region of the etching stop structure 7 in such a way that the sacrificial material layer 01 projects beyond the contour of the etching stop structure 7 at least in regions.

[0082] In Fig. 10, a method for producing a microelectromechanical device 1 according to a fourth embodiment is explained below using an intermediate state. Figs. 11a, 11b and 11c show different variants of a detailed section marked in Fig. 10, which relates to the transition between the etch stop structure 7 and the adjacent cavity access channel 5. As shown, etching channels 19 can be introduced into the cap substrate 6 in the cavity access channel 5 or adjacent thereto, via which etching channels 19 a rapid removal of the sacrificial material layer 01 in the region of the etch stop structure 7 is enabled. The etching channels 19 can be introduced into the cap substrate 6 in particular as narrow trench structures, which can be well closed superficially. In addition, at least one etching channel can extend beyond a width of the etch stop structure 7, so that, as in Fig.11b, a connecting channel 10 is formed in the cap substrate 6 between the cavity access channel 5 and the cavity 3, thus providing a fluid path into the cavity 3. In this case, the etch stop element 8 of the etch stop structure 7 does not have to be connected to the cap substrate 6 via fastening elements 11 with recesses in between in order to create a cavity access; instead, the etch stop element 8 can be connected directly and over its entire surface to the cap substrate 6. According to Fig. 11c, the at least one etching channel 19 can also be provided entirely within a lateral region in the cap substrate 6 defined by the circumferential contour of the etching stop structure 7, and at least one exit channel 22 can be introduced into the etching stop structure 7, which creates a fluid path between the etching channel 19 as a connecting channel 10 to the cavity access channel 5 and the cavity 3.In this embodiment, the etching channel 19 can be at least partially and / or at least superficially closed by material of the first etch stop region 9 immediately after being introduced into the cap substrate. In the variant shown in Fig. 11b and / or in Fig. 11c, it is possible to provide the etch stop element 8 and / or the first etch stop region 9 directly adjacent to the at least one cavity access channel 5 and, for example, to use the material of the first etch stop region 9 applied to the cap substrate 6 to at least superficially close the cavity access channel 5. As a result, the etch stop structure 7 can be designed to be comparatively flat and have a large distance from a connected functional unit 2. Furthermore, the application of a second material layer M2 and the application of a sacrificial material layer O1 can be omitted, so that the manufacturing process can be simplified.

[0083] As a precaution, it is pointed out that the method steps and variants described above according to the first to fourth embodiments can be combined with each other as desired.

[0084] The methods and devices described above enable simple and process-reliable production as well as safe and long-lasting operation of microelectromechanical devices.

Claims

Claims 1. Method for producing a microelectromechanical device (1) with a functional unit (2), at least one cavity (3) and a cap structure (4) delimiting the at least one cavity (3) with at least one cavity access channel (5), wherein the at least one cavity (3) is provided between the cap structure (4) and the functional unit (2), wherein the cap structure (4) is produced by stepwise application and optional structuring of material layers (A1, A2, A3, M1, M2, M3, O1) on a cap substrate (6), the functional unit (2) is connected to the cap structure (4) and the at least one cavern access channel (5) is introduced into the cap structure (4) by etching, wherein during the production of the cap structure (4) an etch stop structure (7) covering an exit of the cavern access channel (5) and projecting into the cavern (3) is produced, said etch stop structure having an etch stop element (8) and a first etch stop region (9) arranged in the etch stop element (8).

2. The method according to claim 1, wherein the first etching stop region (9) is enclosed in the etching stop element (8) in such a way that it is in particular completely surrounded by the etching stop element (8).

3. Method according to claim 1 or 2, wherein at least one connecting channel (10) connecting the cavity (3) to the at least one cavity access channel (5) is produced between the etching stop element (8) and the cap substrate (6) and / or in the etching stop element (8) and / or in the cap substrate (6).

4. Method according to one of the preceding claims, wherein the first etching stop region (9) is formed by means of the etching stop element (8) and / or by means of a fastening element (11) is provided by fastening to the cap substrate (6) and / or to a lateral cavity boundary (20, 20') spaced from the cavity access channel (5).

5. Method according to one of claims 1 to 3, wherein the first material layer (M1) or the first etch stop region (9) of the etch stop element (8) directly adjoins the exit of the at least one cavern access channel (5).

6. Method according to one of the preceding claims, wherein at least one access to a bond pad region (15) and / or to bond pad structures of the cap structure (4) is introduced into the cap structure (4).

7. Method according to one of the preceding claims, wherein the etching stop element (8) is connected to the cap structure (4) and / or to a lateral cavity boundary (20, 20') by means of at least one fastening element (11).

8. The method according to claim 7, wherein, for producing the fastening element (11), a sacrificial material layer (01) is applied and removed again in regions, and wherein at least one region in which sacrificial material has been removed is at least partially filled by a material layer (M1) applied to the sacrificial material layer (01).

9. Method according to one of the preceding claims, wherein a cap substrate recess (12) is produced before and / or during and / or after the creation of the cavern access channel (5).

10. Method according to one of the preceding claims, wherein a second etching stop region (13) is produced on the etching stop structure (7) and by subsequently applying at least one further material layer (M3) a lateral cavity boundary (20, 20') of the Cap structure (4) is increased such that the height (hi) of the lateral cavity boundary (20, 20') of the cap structure (4) (hi) relative to the cap substrate (6) is greater than the height (h2) of the etch stop structure (7) relative to the cap substrate (6).

11. Method according to one of the preceding claims, wherein during and / or after the production of the etching stop structure (7) a cavern depression (14) is introduced into the cap substrate (6) of the cap structure (4).

12. Microelectromechanical device (1) with a functional unit (2), at least one cavity (3) and a cap structure (4) delimiting the at least one cavity (3) and having at least one cavity access channel (5), wherein the at least one cavity (3) is provided between the cap structure (4) and the functional unit (2), wherein the cap structure (4) has a cap substrate (6) and at least one material layer (A1, A2, A3, M1, M2, M3, O1) applied thereon and optionally structured, wherein the cap structure (4) has an etching stop structure (7) covering the exit of the cavity access channel (5) and projecting into the cavity (3), said etching stop structure having an etching stop element (8) and a first etching stop region (9) arranged in the etching stop element (8).

13. Microelectromechanical device (1) according to claim 12, wherein the first etching stop region (9) is in particular completely surrounded by the etching stop element (8).

14. Microelectromechanical device (1) according to claim 12 or 13, wherein the cap structure (4) has at least one connecting channel (10) connecting the cavity (3) to the at least one cavity access channel (5) between the etching stop element (8) and the cap substrate (6) and / or in the cap substrate (6).

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