Method for producing a microelectromechanical device comprising a cap structure, and microelectromechanical device comprising a cap structure

Abstract

The invention relates to a method for producing a microelectromechanical device (1) comprising a functional unit (2), a cavity (3), and a cap structure (4) that covers the cavity (3) and has at least one cavity access (5), in which method the cap structure (4) is produced by sequentially depositing material layers on a cap substrate (6), the functional unit (2) is attached to the cap structure (4), and at least one inlet channel (7) in the at least one cavity access (5) is formed in the cap structure (4) by means of etching, wherein, during the production of the cap structure (4), at least one inlet channel (7), at least one outlet channel (9) opening into the cavity (3), and at least one lateral channel (8) running parallel to a surface of the cap substrate (6) and opening into the at least one inlet channel (7) and into the at least one outlet channel (9) are formed in the cap structure (4), and wherein, during the production of the cap structure (4), a first etch-stop structure (10a) is formed in order to limit the insertion depth of the inlet channel (7) into the cap structure (4). The invention also relates to a microelectromechanical device (1).

Description

[0001] Description

[0002] title

[0003] Method for producing a microelectromechanical device with a cap structure and microelectromechanical device

[0004] WITH CAP STRUCTURE

[0005] The invention relates to a method for producing a microelectromechanical device and a microelectromechanical device.

[0006] State of the art

[0007] Microelectromechanical devices, also called MEMS devices, and methods for their manufacture are known from the prior art.

[0008] US 10 626 008 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.

[0009] 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.

[0010] US 10 407 299 B2 relates to a MEMS sensor, for example, an inertial sensor, comprising a bottom cap wafer and a top cap wafer, between which the sensor structure is formed. The MEMS sensor can have multiple cavities, wherein at least one cavity can be at ambient pressure via a vent channel. Furthermore, a method for manufacturing the sensor is described.

[0011] Disclosure of the Invention According to the features of independent claim 1, a method for producing a microelectromechanical device with a functional unit, a cavity, and a cap structure covering the cavity with at least one cavity access is proposed, in which the cap structure is produced by gradually applying material layers to a cap substrate, the functional unit is connected to the cap structure, and at least one input channel of the at least one cavity access is introduced into the cap structure by etching, wherein during the production of the cap structure, at least one input channel, at least one output channel opening into the cavity, and at least one lateral channel running parallel to a surface of the cap substrate and opening into the at least one input channel and the at least one output channel are introduced into the cap structure,and wherein, during the production of the cap structure, a first etch stop structure is introduced into the cap structure to limit the insertion depth of the at least one input channel.

[0012] By producing a cavity access having an input channel, an output channel, and a lateral channel running parallel to a surface of the cap substrate and opening into the at least one input channel and the at least one output channel, and by providing a first etch stop structure to limit the insertion depth of the at least one input channel, the functional unit of the microelectromechanical device is protected from a potentially unwanted etching attack during the insertion of the input channel. The first etch stop structure reliably limits the etching depth during the insertion of the input channel, and the input channel is inserted into the cap structure only up to the intended etch stop structure, without the input channel directly passing through the cavity, so that the cavity access can be produced in a way that protects the functional unit from an etching attack.Furthermore, a high degree of design freedom is enabled when designing the cavern access. For example, the opening of the exit channel into the cavern can be selected independently of the position of the entrance opening of the entrance channel on the surface of the cap structure, allowing both positions and the respective geometric shape of the channels to be optimized according to individual requirements. Furthermore, at least one geometric size can be generated for at least one section of the cavern access independently of the minimum feature size that can be produced or resolved using the photolithography process used.The first etch stop structure introduced into the cap structure can also facilitate further manufacturing steps of the device manufacturing process, for example, making it easy and reliable to create recesses in a cavity region and / or in a bond pad region, or to create a through-hole penetrating the cap structure in a bond pad region, or to save time when simultaneously structuring different regions of the device, possibly subject to an ARDE (Aspect Ratio Dependent Etching) effect. The introduction of etch stop structures can thus also increase design freedom during the manufacture of the cap structure. Furthermore, for example, by introducing at least a first etch stop structure, thinner and / or fewer material layers can be used to construct the cap structure, which are effectively protected from etching attack by the etch stop structure.

[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 have, for example, one or more movable microstructures in the sensing region, which are configured to perform the sensor function of the functional unit. The movable microstructure can be designed, for example, 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 be designed, for example, 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, for example, enables the mobility of a microstructure of the sensing area within the cavity and enables interaction of the microstructure with the environment of the microelectromechanical device via the cavity access, for example, to detect ambient pressure. The microelectromechanical device can optionally have additional cavities, for example, 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 area of ​​the functional unit from mechanical impacts or undesirable environmental influences, and enables controlled and limited interaction of the sensing area with the environment via a defined cavity access. The cap structure is produced layer by layer by applying material layers to a flat cap substrate, whereby the material layers can essentially form layer planes with a larger areal extension parallel to the cap substrate surface than their extension across the layer height. The material layers can be structured in individual manufacturing steps to create specific functional cap areas or to prepare for further manufacturing steps.

[0017] The input and output channels incorporated into the cap structure can, for example, be configured orthogonally to the layer planes, while the at least one lateral channel can be configured to run parallel to the layer planes and / or parallel to the cap substrate surface. Channels running parallel to the layer planes, for example the at least one lateral channel connecting the at least one input channel and the at least one output channel, can be configured as buried cavity structures. Buried cavity structures are enclosed free spaces in layered structures that are created using special manufacturing techniques. The lateral channel can form a lateral branch on the circumference of the input channel and / or the output channel.In a plane parallel to the surface of the cap substrate, the lateral branch can open into a side wall of the input channel and / or the output channel at a right angle or at an acute or obtuse angle. The lateral channel can connect the input and output channels to one another, for example, to enable a fluid connection between an input of the input channel on the surface of the cap structure and an output of the output channel into the cavity. The input can be laterally offset from the output, wherein the offset can correspond to the length of the lateral channel. A lateral offset can, for example, be an offset along a layer plane perpendicular to the central axis of the input channel and / or the output channel.In principle, however, according to further embodiments, it is also conceivable for a plurality of lateral channels to be connected to one another in such a way that the exit channel is aligned with the entry channel and there is no lateral offset between the entry and exit. The entry channel does not open directly into the cavern, but is only indirectly connected to the cavern via at least one lateral channel and at least one exit channel. The entry channel can be designed as a blind hole. The lateral channel can open into the entry channel, for example, at a channel base at the end of the entry channel, or at any position between the channel base and an entry of the entry channel on the surface of the cap structure. The exit channel can be designed as a blind hole.The lateral channel can, for example, open into the exit channel at a channel base at the end of the exit channel or at any position between the channel base and an exit of the exit channel at the cavern. Due to the course of the entry channel, the lateral channel, and the exit channel, the cavern access has at least deflections at the transitions of the respective channel sections, at which a change of direction of a fluid flow through the cavern access occurs. The cavern access can, in a plane perpendicular to the surface of the cap substrate, geometrically correspond to or approximate a Z-shape or a point-mirrored L-shape, for example, and can have any geometric shape in a plane parallel to the surface of the cap substrate.The geometric dimensions and / or shapes of the inlet channel, the lateral channel and / or the outlet channel can be selected such that only gaseous media can flow through the cavern access, while liquids or solid particles above a certain particle size are prevented from entering the cavern. This can be further promoted by the multiple deflection of the cavern access. In principle, the at least one lateral channel can have, at least in some regions, a smaller channel cross-section than the inlet channel and / or the outlet channel. Alternatively, it is conceivable for the lateral channel to have, at least in some regions, a larger channel cross-section than the inlet channel and / or the outlet channel. Depending on the embodiment, the inlet channel can have a larger or smaller channel cross-section than the outlet channel.The at least one lateral channel may have any shape and / or any geometric dimensions in a plane parallel to the surface of the cap substrate.The channel cross-sections of the cavern access, the number of input channels, the number of output channels, the number of lateral channels, the number of connections between lateral channels and the number of lateral channels that open into an input channel and / or output channel can be adapted to the intended type of microelectromechanical device, to the mode of operation of the functional unit and to the respective associated requirements, for example, with small channel cross-sections and / or slot-shaped channel cross-sections, a high level of protection of the cavern against particles and liquids can be offered, or with large channel cross-sections and / or a large number of lateral channels and / or input channels and / or output channels, a low flow resistance can be emphasized.

[0018] To optimize the area of ​​a MEMS device, e.g., a sensor and / or actuator device, the input channel can be arranged in the cap structure above a sensing region of the functional unit. The input 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. 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 made of a robust encapsulation material outside the at least one input channel for improved protection. In this process, an external seal for the input channel is required, and for this purpose, a sufficient covering surface surrounding the input channel for attaching a protective film is required, so that an arrangement of the input channel close to the center is advantageous.

[0019] In principle, the device can also have multiple cavern accesses. In general, a cavern access can, for example, have an input channel, a lateral channel, and an exit channel. It is also conceivable for the cavern access to have multiple input channels that open into a lateral channel. It is also conceivable for the cavern access to have multiple exit channels that open into a lateral channel. It is also conceivable for the cavern access to have multiple lateral channels that open into an input channel. It is also conceivable for the cavern access to have multiple lateral channels that open into an input channel and / or an exit channel.It is also conceivable for several lateral channels to be interconnected, with at least one lateral channel of the several lateral channels being able to open into an input channel and at least one lateral channel of the several lateral channels being able to open into an output channel. Thus, several cavern accesses, several input channels, and / or several output channels can also be provided, which can optionally open into a lateral channel. Furthermore, any combination of the previously described variants is possible.

[0020] The terms "inlet" and "outlet" as well as "inlet channel" and "outlet channel" are used merely to facilitate understanding of the device and method. It is of course also possible that, depending on the design and application of the microelectromechanical device, the cavity access can alternatively or additionally form a vent, allowing fluid to enter the cavity from the outlet channel and exit the cavity at the surface of the cap structure. The cavity access can thus also allow bidirectional fluid movement between the environment and the cavity.The application of material layers, which can in particular be semiconductor-based material layers such as monocrystalline or polycrystalline silicon layers or layers of silicon compounds such as silicon dioxide (SiCh) or silicon nitride (SiS1^), can be carried out, for example, by deposition using deposition processes known in semiconductor technology. The material layers are applied to a substrate, also called a wafer, for example to a silicon substrate. A material layer can be applied continuously to the substrate or to an already applied material layer, or only in sections, for example by masking at defined positions or sections. Structuring or the introduction of cavities or depressions is possible, for example, using etching processes.For example, introduced cavities can be closed again with an additional layer of material, creating a buried cavity structure. The etching processes can advantageously be carried out using dry etching methods, such as plasma etching. However, wet-chemical etching processes can also be used in principle. 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 structure and using a wafer bonding process known in semiconductor technology. The bonding 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 structure can be designed as a bonding frame. The bonding 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 bonding structure and the capping structure, at least one dielectric layer containing, for example, silicon (Si), aluminum (Al), titanium (Ti), tantalum (Ta), oxygen (O), and / or nitrogen (N), and / or at least one adhesion-enhancing layer containing, for example, tantalum (Ta), titanium (Ti), tungsten (W), nickel (Ni), nitrogen (N), and / or platinum (Pt), or a layer combination of layers containing the aforementioned materials can be provided, which can optionally also be used to produce electrical conductor tracks. The aforementioned chemical elements can also be present as chemical compounds in the layers, for example as silicon dioxide (SiCh), silicon nitride (SiSn), silicon oxynitride (SiON), titanium oxide (TiCh), tantalum oxide (Ta2O3), 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 a further 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., for example, viewed parallel to the substrate surfaces, the microelectromechanical device can, for example, comprise 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 that can be electrically connected, for example, to an evaluation circuit by means of wire bonds.

[0023] The etch stop structure can be a material layer or a laterally delimited layer section of a material layer that preferably has a higher etch selectivity or etch resistance than adjacent material layers and can prevent an etching process or etching progress into material layers protected by the etch stop structure. For example, the material layer can be chemically and / or physically more resistant than adjacent layers and / or have a significantly lower etch rate than adjacent layers. The etch stop structure is advantageously matched to the etching processes and etching media used to produce the cap structure. Alternatively, it is also possible, for example, to select a material layer for the etch stop structure that is resistant to a wet-chemical and / or gaseous etching process, for example, a plasma etching process or a gas-phase etching process.The first etch stop structure can be incorporated into the cap structure such that it is opposite a designated entrance opening of the input channel and, after the input channel has been created, limits the channel length or depth, for example, forming a channel base at the end of the input channel. The etch stop structure can be effective on both sides, making it advantageous not only for the creation of the input channel, but also, for example, for the reliable and easy creation of recesses in the cap structure. For example, recesses of different depths in the bond pad area and sensing area can be created easily and reliably using the first etch stop structure.

[0024] According to one embodiment, during the production of the cap structure, a second etch stop structure can be introduced into the cap structure in the region of the at least one exit channel. The second etch stop structure can facilitate production steps of the cap structure prior to the introduction of the exit channel and enables improved monitoring and control of the insertion depth of the exit channel. The second etch stop structure can form a preliminary etch stop structure that facilitates the structuring of material layers before the exit channel is introduced. In this embodiment, the exit channel can be introduced by etching into the cap structure and through the etch stop layer. The second etch stop structure can optionally limit a preliminary etch depth during the production of the exit channel.In principle, it is conceivable to introduce further etch stop structures into the cap structure during production in order to, for example, further facilitate the creation of further depressions, for example cavity depressions or bond pad area depressions explained below, and to make them process-reliable.

[0025] According to one embodiment, the first etch stop structure and the second etch stop structure can be produced as a continuous etch stop layer. The first etch stop structure and the second etch stop structure can thus form a common etch stop layer and merge directly into one another. The continuous etch stop layer simultaneously enables an etch stop for the at least one input channel, the at least one output channel, and other regions of the cap structure, so that further processing of the cap structure can be facilitated and designed with process reliability. Furthermore, a very flat cap structure can be achieved with few material layers, for example, with only one silicon dioxide layer and one silicon layer.

[0026] According to one embodiment, the first and / or second etch stop structure can be created with a silicon dioxide layer. This creates an etch stop structure that is particularly easy to manufacture and at the same time very effective. The silicon dioxide layer can, for example, have high chemical etch resistance in a plasma etching process, so that the introduction of the input channel and / or optionally also the output channel can be controlled and the introduction depth can be reliably controlled or limited by the etch stop structure. In a subsequent process step, the etch stop structure can optionally be at least partially removed.

[0027] According to one embodiment, at least one channel support structure and / or at least one channel blocking structure can be created in the at least one lateral channel. A channel support structure can be a structure extending in the channel space over the entire height of the lateral channel, for example a columnar structure, which contributes to improved stability of the cap structure. A channel blocking structure can be a structure extending into the channel space of the lateral channel, for example a base-shaped structure, which causes a section-wise channel narrowing of the lateral channel. With a channel blocking structure, the cavern access can be blocked, for example, for liquids or solid particles above a certain particle size, thus preventing contamination of the cavern and the sensitive microstructures of the functional unit. The channel blocking structure can form a filter region of the cavern access.The multiple redirection of the cavern access via the angled channel course further promotes the retention of liquids and particles.

[0028] According to one embodiment, the lateral channel can be created in the cap substrate of the cap structure. This allows for simple production of the lateral channel by machining the cap substrate before applying material layers to the cap substrate. Furthermore, a flat overall structure of the cap structure can be achieved.

[0029] According to one embodiment, the at least one lateral channel can be created by applying, structuring, and at least partially removing at least one sacrificial material layer. The sacrificial material layer can be a silicon dioxide layer, for example. After applying the sacrificial material layer, which can optionally also be applied in multiple layers and / or can consist of multiple layers, a material layer, for example a silicon layer, can be applied to the sacrificial material layer and at least one etching access can be introduced into the material layer consisting of silicon in order to enable the subsequent removal of the sacrificial material layer. The at least one etching access can be created, for example, by microperforating the material layer consisting of silicon in order to be able to easily close the etching accesses again after the sacrificial material layer has been removed.

[0030] In principle, it is not impossible to provide multiple lateral channels at different layer heights and / or at least one lateral channel in the cap substrate and / or one lateral channel in the material layer structure. With multiple lateral channels, the flow resistance in the cavern access can be advantageously reduced. Furthermore, at least one additional lateral channel can serve as an alternative channel if another lateral channel is blocked, for example, by particle accumulation or has reduced permeability.

[0031] According to a further embodiment, after structuring a first sacrificial material layer, in particular immediately after structuring a first sacrificial material layer, at least in a region in which the first sacrificial material layer was removed, a second sacrificial material layer, a first silicon layer, an etch stop layer, and a second silicon layer can be applied successively such that the etch stop layer is substantially completely surrounded by the first silicon layer and / or the second silicon layer. The etch stop layer can be made of silicon dioxide, for example. With the described embodiment, the generation of the lateral channel can be meaningfully and efficiently linked to the formation of an etch stop structure in the lateral channel.The first sacrificial material layer, which may be made of silicon dioxide, for example, can be structured after application such that a sacrificial material-free region is created in the region of an input channel, which region is preferably formed centrally to the input channel and whose outer circumference can extend circumferentially at a defined distance from the outer circumference of the input channel. After structuring the first sacrificial material layer, the second sacrificial material layer is applied, which may be made of silicon dioxide. The thickness of the second sacrificial material layer can later be used to set a reduced height of the at least one lateral channel in a region in which the first sacrificial material layer was removed. Optionally, after application of the second sacrificial material layer, the first and second sacrificial material layers can be structured such that sacrificial material-free regions are created, which can be used to produce later channel support structures.In a subsequent step, a first silicon layer is applied, and the sacrificial material-free regions are thus at least partially removed. A silicon dioxide layer is then applied. The resulting surface can be planarized, for example, using a CMP step such that the silicon dioxide layer outside a sacrificial material-free region in the first sacrificial material layer is removed from the surface of the first silicon layer and only remains on the first silicon layer within a sacrificial material-free region in the first sacrificial material layer, creating a flat surface. The silicon dioxide layer remaining on the first silicon layer in a sacrificial material-free region of the first sacrificial material layer can later be used as a first etch stop structure and / or as a second etch stop structure.In a further method step, a second silicon layer can be applied and structured together with the first silicon layer in such a way that at least one etching access to the first sacrificial material layer and the second sacrificial material layer is created. By applying a second silicon layer, the material of the silicon dioxide layer remaining in a sacrificial material-free region of the first sacrificial material layer on the first silicon layer is completely enclosed with silicon and thus protected from etching attack during the removal of the first sacrificial material layer and the second sacrificial material layer.In a further step, the at least one etching access through the first silicon layer and the second silicon layer can be closed by depositing a third silicon layer after removing the first sacrificial material layer and the second sacrificial material layer, so that at least one lateral channel can be created, followed by the production of a bonding structure. By jointly structuring the first silicon layer, the second silicon layer, and the third silicon layer, at least one exit channel can subsequently be created, which opens into at least one lateral channel. Alternatively, structuring of the first and second silicon layers and the deposition of a third silicon layer can be omitted, and after producing the at least one exit channel, the first and second sacrificial material layers can be removed. Optionally, a bonding pad region recess can also be created in the region of bonding pad structures.

[0032] In principle, it is conceivable that the sacrificial material layers mentioned in connection with the previously described embodiments can also be provided outside of lateral channels and can be retained there, for example under bond structures.

[0033] According to an advantageous embodiment, a cavity recess and / or a bond pad region recess and / or a through-opening in the region of bond pad structures can be introduced into the cap structure during the production of the cap structure. The cavity recess and / or the bond pad region recess can be introduced, in particular etched, into already applied material layers of the cap structure. A cavity recess can enable an enlargement of the cavity formed between the cap structure and the functional unit, thus achieving an enlargement of the enclosed cavity volume. This can, for example, increase the freedom of movement of a movable microstructure of the functional unit, enabling, for example, a greater deflection of a microstructure.In addition, a larger cavity, for example for a microelectromechanical device designed as a sensor device, can reduce the time-dependent effect of gas leaks and / or outgassing from the layer system, such as an increase in the internal pressure of the cavity per unit time, thus increasing the service life of the sensor device. 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 the input channel has been created in order to be able to create free access to bond pad structures. An opening that completely penetrates the cap structure can be provided in the region of bond pad structures.

[0034] According to one embodiment, during production of the cap structure, a plurality of lateral channels running parallel to a surface of the cap substrate can be introduced into the cap structure. At least one lateral channel can open into the inlet channel and the outlet channel. Alternatively, a plurality of lateral channels can open into an inlet channel and / or an outlet channel. By having a plurality of lateral channels, the flow resistance in the cavern access can be advantageously reduced, which can be beneficial, for example, for sensor devices for detecting dynamic variables, wherein a filter function, for example against particles, can also advantageously be achieved or maintained. In addition, a lateral channel can serve as an alternative channel if another lateral channel is blocked, for example, by an accumulation of particles or has reduced permeability.As already explained, the lateral channels can be provided, for example, at different layer heights and / or in the cap substrate and / or in a material layer. However, it may be advantageous from a manufacturing perspective to create multiple lateral channels in one cap substrate plane or in one layer plane, so that the lateral channels can be incorporated at a single height within the layer structure. The lateral channels can, for example, be arranged opposite one another or adjacent to one another and be interconnected via the input channel, the output channel, additional channels, and / or the selected channel path.The lateral channels can converge at an angle, which can be, for example, a vertical angle or an acute or obtuse angle, and flow into one another, or can be interconnected and / or enter a wall of the inlet channel and / or the outlet channel at an angle, which can be, for example, a vertical angle or an acute or obtuse angle. For example, several lateral channels can converge in a cross-shaped or star-shaped manner and flow into one another, and / or flow into the inlet channel and / or the outlet channel in a cross-shaped or star-shaped course. In principle, there is a high degree of design freedom in the arrangement of several lateral channels in relation to one another and their connection to one another. At least one inlet and / or outlet channel can branch off from each of the lateral channels, for example in a branch-like manner, and for example, a pressure access to the cavern can be created.However, it is also conceivable for several lateral channels to open into a common input channel and / or output channel and / or for several input channels and / or output channels to open into a lateral channel. The lateral channels can also be interconnected outside or away from an input channel and / or an output channel. The position of the exit into the cavity of the at least one output channel can be freely selectable; for example, the output channel can open into the cavity offset from a movable microstructure or a sensing area of ​​the functional unit. The output channel can, for example, open into the cavity at an introduced cavity recess of the cap structure or away from such a cavity recess.

[0035] According to one embodiment, at least two lateral channels can be connected to each other by at least one connecting channel and / or open into each other. This can advantageously further reduce the flow resistance in the cavern access.

[0036] According to one embodiment, at least one first etch stop structure and / or at least one first channel blocking structure can be produced at a distance from the cap substrate, and at least one second etch stop structure and / or at least one second channel blocking structure can be produced directly on the cap substrate. Due to the different positions of the etch stop structures, they can advantageously influence the control of etching processes in different manufacturing steps. Due to the different positions of channel blocking structures and the associated labyrinth effect, the cavity access can be protected even more reliably against particle or liquid ingress.

[0037] After the input channel has been introduced into the cap structure, the input 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.

[0038] 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.

[0039] According to the features of independent claim 13, a microelectromechanical device is further proposed with a functional unit, a cavity and a cap structure covering the cavity with at least one cavity access, wherein the cavity access has at least one input channel, at least one output channel opening into the cavity and at least one lateral channel running parallel to a surface of the cap substrate and opening into the at least one input channel and the at least one output channel, wherein the at least one input channel in the cap structure is delimited by a first etch stop structure in the input depth.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 a cavern access with multiple deflections, for example during manufacture from process influences, but also during operation from undesirable or excessive environmental influences.

[0040] The device may also have further features presented in connection with the method described above, for example a second etch stop structure in the region of the at least one output channel, a first and / or second etch stop structure formed from a silicon dioxide layer, at least one lateral channel formed in the cap substrate and / or in the material layers of the cap structure and running parallel to a surface of the cap substrate, at least one channel support structure and / or at least one channel blocking structure in the at least one lateral channel, a plurality of lateral channels opening into the input channel and / or output channel, lateral channels that are additionally interconnected outside of an input channel and / or an output channel by at least one channel, a plurality of input channels and / or output channels opening into a lateral channel,a cavity depression and / or a depression in the bond pad area and / or a through-opening in the area of ​​bond pad structures in the cap structure.,

[0041] 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 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.

[0042] 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”.

[0043] The invention permits various embodiments and is explained in more detail below using exemplary embodiments with the accompanying drawings. They show:

[0044] Fig. 1a - a schematic sectional view of a microelectromechanical device according to a first embodiment;

[0045] Fig. 1b - a schematic plan view of a section of the device marked with a dot-dash line in Fig. 1a;

[0046] Fig. 2a-2g - using schematic sectional representations, method steps for producing the microelectromechanical device according to a first embodiment;

[0047] Fig. 3a-3b - schematic sectional views showing method steps for manufacturing the microelectromechanical device according to a second embodiment; Fig. 4a-4d - schematic sectional views showing method steps for manufacturing the microelectromechanical device according to a third embodiment;

[0048] Fig. 5 - a schematic sectional view of a microelectromechanical

[0049] Device according to a fourth embodiment;

[0050] Fig. 6 - a schematic sectional view of a method step for producing the microelectromechanical device according to a fifth embodiment.

[0051] Figure 1 shows a schematic sectional view of a microelectromechanical device 1 according to a first embodiment. The device 1 is embodied, by way of example, as a sensor device and has a sensing region 15 for performing a sensor function and a bond pad region 16 for providing an external electrical connection, for example to an ASIC evaluation circuit. The device 1 has a functional unit 2, which, for example, has a movable microstructure as a measuring means for measuring ambient conditions, for example an ambient pressure. The functional unit 2 can alternatively or additionally have an ASIC for signal processing. The functional unit 2 is connected mechanically and / or at least partially electrically conductively and / or at least partially electrically non-conductively to a cap structure 4 of the device 1 via bond structures 17.The cap structure 4 protects the functional unit 2, at least in part, from mechanical impacts as well as from specific or excessive environmental influences. A cavity 3 is formed between the cap structure 4 and the functional unit 2, which cavity 3 is at least partially enclosed by at least one bond structure 17. The cavity 3 forms a measuring chamber for recording ambient conditions by means of the functional unit 2. The cap structure 4 has a cavity access 5, through which the cavity 3 can interact with the environment via a ventilation path 18 and through which, for example, fluid or gas flows can flow into the cavity 3 or back into the environment. As shown, the cavity access 5 is not designed as a through-opening, but rather as a multiply angled channel system.The cavern access 5 has at least one input channel 7, at least one output channel 9 connected to the cavern 3, and at least one lateral channel 8 running parallel to a surface of the cap substrate 6, which opens into the at least one input channel 7 and the at least one output channel 9. The cap structure 4 is formed by optionally structured material layers applied successively to a cap substrate 6, which are illustrated in Figure 1 by way of example as a first silicon layer 19a, a silicon dioxide layer 20, and a second silicon layer 19b. The lateral channels 8 are formed in the cap substrate 6. As can be seen from Figure 1, a first etch stop structure 10a in the region of the at least one input channel 7 and optionally a second etch stop structure 10b in the region of the at least one output channel 9 are introduced into the layer structure of the cap structure 4.The first etch stop structure 10a can limit the insertion depth of the at least one input channel 7 during the etching of the at least one input channel 7. The optional second etch stop structure 10b can form a preliminary etch stop structure that facilitates the structuring of material layers before the output channel 9 is introduced. The first etch stop structure 10a and optionally the second etch stop structure 10b can enable simple and process-reliable production of the device 1.

[0052] Figure 1b shows a schematic plan view of the section of the device 1 marked with a dash-dotted line in Fig. 1a in the region of an input channel 7. Figure 1b shows that a plurality of lateral channels 8 can advantageously be introduced into the device 1, which, according to the exemplary embodiment shown, run cross-shaped towards the input channel 7 and can open into it. By forming a plurality of lateral channels 8, the flow resistance of the cavern access 5 can be reduced and / or the effects of a lateral channel 8 closed by foreign substances on the function of the component can be reduced. Furthermore, Figure 1b indicates that the first etch stop structure 10a is placed in the region of the input channel 7, which, as shown in Figure 1a, limits the channel depth of the input channel 7 during the etching of the input channel 7.

[0053] A method for manufacturing the device 1 is described below with reference to Figures 2a to 2g. Figures 2a to 2f show the manufacture of the cap structure 4, while Figure 2g shows the subsequent connection of the functional unit 2 and the subsequent introduction of the input channel 7.

[0054] In Figure 2a, in a first manufacturing step, lateral channels 8 are introduced into a cap substrate 6, for example a silicon substrate, for example by etching.

[0055] In Figure 2b, the produced lateral channels 8 are closed with a first silicon layer 19a in a second manufacturing step, so that the lateral channels 8 form a buried channel structure.

[0056] In Figure 2c, in a third manufacturing step, a silicon dioxide layer 20 is applied to the first silicon layer 19a and structured such that in a region of the later at least one input channel 7 and optionally in a region of the later at least one output channel 9, individual sections of the silicon dioxide layer 20 remain, which form a first etch stop structure 10a and optionally a second etch stop structure 10b.

[0057] In Figure 2d, a second silicon layer 19b is applied and optionally patterned in a fourth manufacturing step. In a fifth manufacturing step, also shown in Figure 2d, bonding structures 17 are applied to the second silicon layer 19b, which enable a subsequent mechanical and / or at least partially electrically conductive and / or at least partially electrically non-conductive connection of the cap structure 4 to the functional unit 2. Optionally, the second silicon layer 19b can be planarized using a CMP process.

[0058] Figure 2e shows a sixth manufacturing step in which at least a first output section of the at least one output channel 9 and optionally a cavity recess 13 and a bond pad region recess 14 are created. The at least one second etch stop structure 10b allows the output section of the at least one output channel 9, the cavity recess 13, and the bond pad region recess 14 to be introduced reliably and with a high degree of design freedom, without causing an uncontrolled etching attack on the silicon layers 19a, 19b or the cap substrate 6.

[0059] In Figure 2f, in a seventh manufacturing step, the exit section of the at least one exit channel 9 is further deepened by at least partially removing the silicon dioxide layer 20 and the first silicon layer 19a until it opens into a lateral channel 8 and the at least one exit channel 9 is completely formed.

[0060] Figure 2g shows that, according to an eighth manufacturing step, the functional unit 2 can be connected to the cap structure 4 via the bond structures 17, for example, by applying a wafer bonding process. After the functional unit 2 has been connected to the cap structure 4, the functional wafer of the functional unit 2 and / or the cap substrate 6 of the cap structure 4 can optionally be thinned using a grinding and / or polishing process. Subsequently, additional recesses can optionally be introduced into the functional and / or cap wafer. In the area of ​​bond pad structures 22, by removing cap material and producing at least one through-opening 23, for example, bond pad structures 22 can be made accessible, which can be electrically contacted via wire bond connections and enable an electrical connection to an external ASIC evaluation circuit.In a ninth manufacturing step, the at least one input channel 7 is introduced into the cap structure 4, wherein the insertion depth is advantageously limited by the first etch stop structure 10a. The introduction of the at least one input channel 7 advantageously occurs subsequent to the previously described steps in order to protect the cavity 3 and the functional unit 2 from undesirable process influences caused by the input channel 7 during the manufacture of the device 1.

[0061] Figures 3a and 3b show a method for manufacturing the microelectromechanical device 1 according to a second embodiment. According to the second embodiment, the lateral channels 8 are not introduced into the cap substrate 6 of the cap structure 4, but are created by applying and subsequently locally removing a sacrificial material layer 21 in the layer structure of the cap structure 4. The sacrificial material layer 21 can be formed, for example, from silicon dioxide. The height of the sacrificial material layer 21 can be selected accordingly depending on the desired channel width and the desired channel cross-sectional area.

[0062] According to Figure 3a, in a first manufacturing step, the sacrificial material layer 21 was applied to the cap substrate 6 and structured for the subsequent manufacturing steps. In a second manufacturing step, a first silicon layer 19a is applied and structured, wherein during the structuring, a portion of the sacrificial material layer 21 is exposed and, for example, an etching access to the sacrificial material layer 21 is created. Furthermore, the first silicon layer 19a can optionally be planarized by applying a CMP step before structuring. Furthermore, channel support structures 11 can be formed with the first silicon layer 19a. In Figure 3a, for example, a microperforation of the first silicon layer 19a adjacent to the sacrificial material layer 21 can be seen, which enables removal of the sacrificial material layer 21 in a third manufacturing step.After the removal of the sacrificial material layer 21, the etching accesses in the first silicon layer 19a are closed again in a fourth manufacturing step.

[0063] Figure 3b shows further processing analogous to the second to eighth manufacturing steps of the method described in connection with Figures 2b to 2f. For example, a second silicon layer 19b, a silicon dioxide layer 20 for forming the etch stop structures 10a, 10b, a third silicon layer 19c, and the bond structures 17 were successively applied to the first silicon layer 19a, and the at least one exit channel 9 was created, which opens into at least one lateral channel 8. The creation of the etch stop structures 10a, 10c and / or the bond structures 17 involves the deposition and structuring of a layer and / or a layer system. Optionally, the second silicon layer 19b and / or the third silicon layer 19c can also be additionally planarized and / or structured after the respective deposition.In an alternative embodiment, structuring of the first silicon layer 19a and deposition of the second silicon layer 19b can be omitted, and after the production of the at least one exit channel 9, the sacrificial material layer 21 in the at least one lateral channel 8 can be removed. Figures 4a to 4d show a method for producing the microelectromechanical device 1 according to a third embodiment. The third embodiment, like the method described with reference to Figures 3a and 3b, is fundamentally based on the application and subsequent removal of sacrificial material layers 21a, 21b. A possible intermediate state of the cap structure 4 after the application and structuring of material layers and after the removal of the sacrificial material layers 21a, 21b is shown by way of example in Figure 4a.In a first method step, a first sacrificial material layer 21a made of silicon dioxide was applied and structured in such a way that a silicon dioxide-free region is created in the region of an input channel 7, which region is preferably formed centrally to the input channel 7 and whose outer circumference extends circumferentially at a defined distance from the outer circumference of the input channel 7. After the first sacrificial material layer 21a made of silicon dioxide has been structured, a second sacrificial material layer 21b made of silicon dioxide is deposited. The thickness of the second sacrificial material layer 21b can later be used to adjust a reduced height of the at least one lateral channel 8 in a region in which the first sacrificial material layer 21a was removed.Optionally, after the application of the second sacrificial material layer 21b made of silicon dioxide, the first sacrificial material layer 21a and the second sacrificial material layer 21b can be structured in such a way that silicon dioxide-free regions are created which serve to produce later channel support structures 11.

[0064] In a subsequent second method step, a first silicon layer 19a was applied, and silicon dioxide-free regions were at least partially filled therewith. In a third step, a silicon dioxide layer 20 is then applied, and the resulting surface is planarized using a CMP step such that the silicon dioxide layer 20 is removed from the surface of the first silicon layer 19a outside a silicon dioxide-free region in the first sacrificial material layer 21a and remains on the first silicon layer 19a only within a silicon dioxide-free region in the first sacrificial material layer 21a, creating a flat surface. The silicon dioxide layer 20 remaining on the first silicon layer 19a in a silicon dioxide-free region of the first sacrificial material layer 21a can later be used as the first etch stop structure 10a and / or as the second etch stop structure 10b.In a fourth method step, a second silicon layer 19b can be applied and structured together with the first silicon layer 19a such that at least one etching access to the first sacrificial material layer 21a and the second sacrificial material layer 21b is created. By applying a second silicon layer 19b, the material of the silicon dioxide layer 21b remaining in a silicon dioxide-free region of the first sacrificial material layer 21a on the first silicon layer 19a is completely enclosed with silicon and thus protected from etching attack during the removal of the first sacrificial material layer 21a and the second sacrificial material layer 21b made of silicon dioxide.

[0065] In a fifth method step, the at least one etching access through the first silicon layer 19a and the second silicon layer 19b is closed by depositing a third silicon layer 19c after the removal of the first sacrificial material layer 21a and the second sacrificial material layer 21b, so that at least one lateral channel 8 is produced and the bond structure 17 can subsequently be produced.

[0066] By jointly structuring the first silicon layer 19a, the second silicon layer 19b, and the third silicon layer 19c, at least one exit channel 9 can subsequently be created, which opens into at least one lateral channel 8. In an alternative embodiment, structuring of the first silicon layer 19a and the second silicon layer 19b and the deposition of a third silicon layer 19c can be omitted, and after the production of the at least one exit channel 9, the first and second sacrificial material layers 21a, 21b in the at least one lateral channel 8 can be removed. Optionally, a bond pad region recess 14 can also be created in the region of bond pad structures 22.

[0067] Figure 4b shows, analogously to Figure 4a, a variant in which second etch stop structures 10b can additionally be produced in the region of the later at least one output channel 9 according to the above-described production.

[0068] Figure 4c shows the device 1 after the functional unit 2 has been connected to the cap structure 4 and the at least one input channel 7 has been introduced into the cap structure 4. The method steps carried out for this purpose can, for example, be carried out analogously to the fourth to eighth method steps of the method described in connection with Figures 2d to 2f. Furthermore, it can be seen that by removing the first sacrificial material layer 21a and the second sacrificial material layer 21b in the at least one lateral channel 8, in addition to channel support structures 11, channel blocking structures 12 were also created in the region of the first etch stop structure 10a. These channel blocking structures cause a section-wise narrowing of the lateral channels 8, so that, for example, liquids or solid particles above a defined particle size are prevented from entering the cavity 3 by means of the channel blocking structures 12.

[0069] Figure 4d shows the state of device 1 analogous to Figure 4c with respect to the variant shown in Figure 4b, in which, for example, an additional etch stop structure 10b was created in the region of each of two output channels 9. As can be seen in Figure 4d, the second etch stop structures 10b can also be combined with a channel blocking structure 12.

[0070] Figure 5 shows a variant of the microelectromechanical device 1 and an associated manufacturing method according to a fifth embodiment. The fifth embodiment is essentially based on the fourth embodiment, but has a different arrangement of etch stop structures 10a, 10b and channel blocking structures 12 due to a modified sequence of silicon and sacrificial material layers and their structuring and a suitable layout design. One difference from the fourth embodiment is that the first etch stop structure 10a and a first channel blocking structure 12a are spaced from the cap substrate 6, and the second etch stop structure 10b and a second channel blocking structure 12b are arranged directly on the cap substrate 6, so that the position of possible channel blocking structures 12 in the region of output channels 6 within the layer structure is also different.

[0071] Figure 6 illustrates a sixth embodiment using a selected intermediate state of the manufactured device 1. The sixth embodiment is essentially based on the method described with reference to Figures 2a to 2g, wherein the intermediate state in Figure 6 is comparable to the intermediate state shown in Figure 2f. In the exemplary embodiment shown, the channels 8 produced are closed with a continuous silicon dioxide layer 20 as a continuous etch stop layer. The continuous silicon dioxide layer 20 thus serves to produce a common etch stop structure 10a, 10b for the at least one input channel 7, the at least one output channel 9, and further regions of the cap structure 4, so that further processing of the cap structure can be facilitated and designed with process reliability.In addition, a very flat cap structure 4 can be achieved with few material layers, for example with only a first silicon layer 19a in addition to the silicon dioxide layer 20.

[0072] 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) comprising a functional unit (2), a cavity (3), and a cap structure (4) covering the cavity (3) with at least one cavity access (5), in which the cap structure (4) is produced by gradually applying material layers to a cap substrate (6), the functional unit (2) is connected to the cap structure (4), and at least one input channel (7) of the at least one cavity access (5) is introduced into the cap structure (4) by etching, wherein, during the production of the cap structure (4), at least one input channel (7), at least one output channel (9) opening into the cavity (3), and at least one lateral channel (8) running parallel to a surface of the cap substrate (6) and opening into the at least one input channel (7) and the at least one output channel (9) are introduced into the cap structure (4),and wherein, during the production of the cap structure (4), a first etch stop structure (10a) is introduced into the cap structure (4) to limit the insertion depth of the input channel (7).

2. The method according to claim 1, wherein during the production of the cap structure (4) a second etch stop structure (10b) is introduced into the cap structure (4) in the region of the at least one exit channel (9).

3. The method according to claim 2, wherein the first etch stop structure (10a) and the second etch stop structure (10b) are produced as a continuous etch stop layer.

4. Method according to one of the preceding claims, wherein the first and / or the second etching stop structure (10a, 10b) is produced with a silicon dioxide layer (20).

5. Method according to one of the preceding claims, wherein at least one channel support structure (11) and / or at least one channel blocking structure (12) is produced in the at least one lateral channel (8).

6. Method according to one of the preceding claims, wherein the at least one lateral channel (8) is produced in the cap substrate (6) of the cap structure (4).

7. Method according to one of the preceding claims, wherein the at least one lateral channel (8) is produced by applying, structuring and at least partially removing at least one sacrificial material layer (21a, 21b).

8. The method according to claim 7, wherein after structuring a first sacrificial material layer (21a), in particular immediately after structuring a first sacrificial material layer (21a), at least in a region in which the first sacrificial material layer (21a) was removed, a second sacrificial material layer (21b), a first silicon layer (19a), an etch stop layer (20) and a second silicon layer (19b) are applied one after the other in such a way that the etch stop layer (20) is substantially completely surrounded by the first silicon layer (19a) and / or by the second silicon layer (19b).

9. Method according to one of the preceding claims, wherein during the production of the cap structure (4) a cavern recess (13) and / or a bond pad region recess (14) and / or a through opening (23) in the region of bond pad structures (22) is introduced into the cap structure (4).

10. Method according to one of the preceding claims, wherein during the production of the cap structure (4) a plurality of lateral channels (8) running parallel to a surface of the cap substrate (6) are introduced into the cap structure (4).

11. The method according to claim 10, wherein at least two lateral channels (8) are connected to one another by at least one connecting channel and / or open into one another.

12. Method according to one of the preceding claims, wherein at least one first etch stop structure (10a) and / or at least one first channel blocking structure (12a) is produced at a distance from the cap substrate (6) and wherein at least one second etch stop structure (10b) and / or at least one second channel blocking structure (12b) is produced directly on the cap substrate (6).

13. Microelectromechanical device (1) with a functional unit (2), a cavity (3) and a cap structure (4) covering the cavity (3) with at least one cavity access (5), wherein the cavity access (5) has at least one input channel (7), at least one output channel (9) opening into the cavity (3) and at least one lateral channel (8) running parallel to a surface of the cap substrate (6) and opening into the at least one input channel (7) and into the at least one output channel (9), and wherein the at least one input channel (7) in the cap structure (4) is delimited in the input depth by a first etch stop structure (10a).

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