System and method for packaged MEMS device having embedding arrangement, MEMS die, and grille

A packaged MEMS device may include an embedding arrangement, a MEMS device disposed in the embedding arrangement, a sound port disposed in the embedding arrangement and acoustically coupled to the MEMS device, and a grille within the sound port. Some embodiments relate to a sound transducer component including an embedding material and a substrate-stripped MEMS die embedded into the embedding material. The MEMS die may include a diaphragm for sound transduction. The sound transducer component may further include a sound port within the embedding material in fluidic or acoustic contact with the diaphragm. Further embodiments relate to a method for packaging a MEMS device or to a method for manufacturing a sound transducer component.

TECHNICAL FIELD

Embodiments relate to a packaged MEMS device. Some embodiments relate to a sound transducer component. Some embodiments relate to a method for packaging a MEMS die. Some embodiments relate to a method for manufacturing a sound transducer component.

BACKGROUND

In the technical field of electronic devices and microelectromechanical systems (MEMS), there is a trend towards miniaturization and heterogeneous system integration. Among others, the desire for miniaturization and heterogeneous system integration calls for new packaging technologies which also allow large area processing and 3D integration with potential for low-cost applications. Two major packaging trends in this area are thin film technique and the so called Chip-in-Substrate Package technique (CiSP).

Typically, the main functions of a chip package may be to attach a semiconductor chip or semiconductor die at a printed circuit board (PCB) and to electrically connect the integrated circuit that is implemented on the semiconductor chip/die with the circuit(s) that is/are present on the printed circuit board. The chip may be arranged on an interposer. Furthermore, the package may provide protection for the die against damage and environmental influences (dirt, moisture, etc.).

SUMMARY OF THE INVENTION

A packaged MEMS device is provided that comprises an embedding arrangement, a MEMS device disposed in the embedding arrangement, a sound port disposed in the embedding arrangement and acoustically coupled to the MEMS device, and a grille disposed in the sound port.

According to further embodiments, a packaged MEMS device is provided that comprises an embedding arrangement, a MEMS device disposed in the embedding arrangement, a sound port embedded in the embedding arrangement, and a grille disposed across the sound port. The sound port is acoustically coupled to the MEMS device.

Further embodiments provide a packaged MEMS device that comprises an embedding arrangement, a MEMS device disposed in the embedding arrangement, an opening disposed in the embedding arrangement, and a grille within the opening. The opening is adjacent to the MEMS device.

According to further embodiments, a sound transducer component is provided that comprises an embedding material and a substrate-stripped MEMS die embedded into the embedding material. The MEMS die may comprise a diaphragm for sound transduction. The sound transducer component may further comprise a sound port within the embedding material in fluidic (e.g., acoustic) contact with the diaphragm.

A method for packaging a MEMS device is provided. The method comprises embedding a precursor MEMS die in an embedding arrangement to obtain an embedded precursor MEMS die. The method further comprises creating a grille at a surface of the embedded precursor MEMS die. The method also comprises removing an auxiliary portion of the embedded precursor MEMS die adjacent to the grille to create a sound port within the embedding arrangement.

A method for manufacturing a sound transducer component or a plurality of sound transducer components is provided. The method comprises creating a plurality of spacers at a surface of a wafer comprising a plurality of precursor MEMS dies. Each spacer covers at least a portion of a diaphragm of a corresponding precursor MEMS die. The method also comprises singulating the wafer to obtain a plurality of singulated precursor MEMS dies. The method further comprises embedding a selected number of the plurality of singulated precursor MEMS dies together with the spacers in an embedding arrangement to form a reconstitution wafer. The method comprises removing the plurality of spacers to obtain a plurality of sound ports within the embedding arrangement. The method further comprises singulating the reconstitution wafer, thereby forming or obtaining the sound transducer component(s).

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the following description, a plurality of details are set forth to provide a more thorough explanation of embodiments of the present invention. However, it will be apparent to those skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form rather than in detail in order to avoid obscuring embodiments of the present invention. In addition, features of the different embodiments described hereinafter may be combined with each other, unless specifically noted otherwise.

The present invention will be described with respect to implementation examples in a specific context, namely an embedded MEMS microphone manufactured in a chip embedding process. Embodiments of the invention may also be applied, however, to other MEMS devices, sensors or transducers and to other packaging processes.

FIG. 1shows a schematic cross-section of a sound transducer component100according to a first possible example of implementation. The sound transducer component100may be a packaged MEMS device and comprise a MEMS die110comprising a diaphragm112. The MEMS die110may be a MEMS device or a part of a MEMS device. The sound transducer component may further comprise an embedding material252(also referred to as “main embedding part” for some implementation examples) into which the MEMS die110may be embedded, i.e., the MEMS die may be disposed in the embedding arrangement. For example, the MEMS die110may be embedded by molding in the embedding material252. A cavity160may be formed within the embedding material252. The cavity160may contact the diaphragm112. The cavity160may be in fluidic and/or acoustic contact with the diaphragm112, i.e., a fluid within the cavity160such as air or a gas or a sound wave can reach the diaphragm112via fluidic movement or sound propagation. The fluidic movement may occur through a perforated backplate, a grille, or another similar structure that provides a fluidic and/or acoustic communication between the cavity160and a volume of fluid that is directly adjacent to the diaphragm112. More generally, the cavity160may be in contact or directly adjacent to a sound transducing region of the sound transducer component100. The sound transducing region may typically comprise at least a diaphragm. Furthermore, the sound transducing region may comprise one or more backplate(s) as a counterelectrode for a capacitive sound transducer. In the alternative, the sound transducer component may comprise, for example, a piezoelectric element for transducing a deflection or displacement of the diaphragm into an electrical signal. In some embodiments, the diaphragm112may be implemented as a membrane. The embedding material (encapsulation material)252may be or may comprise a molded compound part or a mold compound. The embedding material may be or may comprise plastic or resin.

In the example of a possible implementation schematically illustrated inFIG. 1, the MEMS die110may comprise a backplate114. The diaphragm112and the backplate114may be arranged substantially parallel to each other with a gap113being interposed between them. The diaphragm112may comprise corrugations116that may be configured to facilitate a deflection/displacement of the diaphragm112. In particular, the corrugations116may serve to provide a substantially parallel displacement of a central portion of the diaphragm112in response to a sound wave impinging on the diaphragm112and causing the diaphragm112to displace. The backplate114may comprise a plurality of anti-sticking bumps118that may be configured to prevent that the backplate114and the diaphragm112adhere to each other in a substantially permanent manner which might make the sound transducer component100unusable. In the example shown inFIG. 1the backplate114may be arranged at a side of the diaphragm112that may be opposite to the cavity160. In alternative examples of implementation the positions of the backplate114and the diaphragm112could be inversed. The backplate114may be perforated and comprise a plurality of holes that allow an arriving sound wave to reach the diaphragm112. The diaphragm112may also comprise a hole to facilitate an equalization of the static pressures in the cavity160and a transducer opening or sound port180, which may be disposed at the opposite side of the diaphragm112than the cavity160. The sound port180may be acoustically coupled to the MEMS device.

The MEMS die110may further comprise at least one of the following: a support structure (not explicitly shown inFIG. 1), a dielectric spacer element (not explicitly shown inFIG. 1) between the diaphragm112and the backplate114, and electrical connections115,117,119that may be configured to provide an electrical contact for the diaphragm112and the backplate114.

The embedding material252may comprises electrical through contacts or “vias”122and124. The embedding material or main embedding part252may comprise a main surface at which a cover layer170may be disposed. The cover layer170may comprise a first redistribution layer or first metallization layer174. The first metallization layer174may be configured to electrically contact the through contacts122,124within the embedding material252and hence the contact pads119,117of the MEMS die110. In the example schematically illustrated inFIG. 1the sound transducer component100may further comprise a grille or grid172disposed in or across the sound port180. The grille172may be configured to provide a mechanical protection and/or a protection against dirt, dust, etc. for the MEMS die110while allowing a sound wave to reach the diaphragm112of the MEMS die via the sound port180. As schematically illustrated inFIG. 1, the grille172may further fulfill a function of electromagnetic interference shielding. To this end, the grille172may be electrically connected to a second metallization layer or redistribution layer176that is also disposed within the cover layer170. The first redistribution layer174may be an underlying redistribution layer relative to the second redistribution layer176. A contact pad178may be electrically connected to the grille172via the second metallization layer176. The second metallization layer176may provide at least one of the following functionalities: shielding of interconnect to ASIC (not shown), shielding of underlying redistribution layer(s), mechanical protection of MEMS layers against particles or touching, and/or potential acoustical low pass filtering of audio band in conjunction with the resulting front cavity.

Upon the integration of the sound transducer component100into a more complex system such as a mobile phone, a smart phone, a digital camera, a digital camcorder, etc., the contact pad178may be connected to a mass (electrical ground) of the surrounding system. In this manner, the grille172may be kept at a substantially constant, well defined electrical potential. The grille172may comprise a plurality of holes, wherein the holes may have a round cross section, a square cross section, a rectangular cross section, an elongate cross section, a hexagonal cross section, a honeycomb arrangement etc.

The sound transducer component100may further comprise a backside cover190configured to close the cavity160. The embedding material252, the cover layer170, and the backside cover190may be part of a package or embedding arrangement for the MEMS die110.

According to some embodiments, a cross-section of the cavity160may be substantially equal to a surface of the MEMS die110. The cross-section of the cavity160is here the cross-section along a section plane parallel to a main surface of the MEMS die110, i.e., substantially parallel to the XY-plane as indicated by the coordinate system inFIG. 1. In other words, a bottom of the cavity160may be substantially completely formed by the MEMS die110. This feature may result from the fact that the MEMS die110as it is present in the finished sound transducer component100is a substrate-free (substrate-stripped) MEMS die. A substrate which was originally part of the MEMS die110prior to the packaging process may be removed during the course of the packaging process, as its function of providing mechanical stability for the MEMS die110during manufacture (in particular during front end processing) can eventually be performed by the embedding material252. The MEMS die110may be embedded by molding into the embedding material252. According to alternative embodiments it is also possible, that only a portion of the original substrate is removed during the packaging process to form the cavity160.

Although not shown inFIG. 1, the sound transducer component (MEMS device)100may further comprise a further die. The further die may be, for example, embedded (e.g., by molding) into the embedding material252. The further die may be, for example, an ASIC (application-specific integrated circuit) that may be used to provide, e.g., a power supply for the sound transducer portion (in particular diaphragm112and backplate114) and/or read-out functionality for providing an electrical signal that corresponds to the sound wave received by the sound transducer component100. For example, the ASIC may be configured to perform an amplification and/or analog-to-digital conversion. At least one of the redistribution layers174and176may be configured to provide an electrical connection between the MEMS die110and the further die (e.g., ASIC). In this context it is noted that the terms “first redistribution/metallization layer” and “second redistribution/metallization layer” are not to be construed as implying a certain stacking order within the cover layer170. In case the cover layer170comprises two or more redistribution/metallization layers, at least one of the redistribution layers (typically the uppermost or outermost redistribution layer) may serve as a shield regarding electromagnetic interference (EMI) for the underlying redistribution layer(s). The grille172may be electrically conductive, at least in part. When being connected to said redistribution layer that is dedicated for EMI shielding or another EMI-dedicated redistribution layer, the grille172may provide EMI shielding for electrical connections between the MEMS die and the further die (e.g., ASIC) and/or for the sound transducing portion of the MEMS die110, i.e., the diaphragm112and the backplate114, for example.

The sound port180may extend within the embedding material252at an opposite surface of the diaphragm112than the cavity160from the diaphragm112. The sound port180may extend to an exterior surface of the sound transducer component and hence to a surrounding environment of the packed MEMS device. The grille172may be mechanically supported either by the embedding material252or by the cover layer170. The sound port180may also extend through the cover layer170. In other words, the packaged MEMS device100may comprise the MEMS device110and the sound port180which is adjacent to the MEMS device110. The packaged MEMS device100may further comprise the embedding arrangement that embeds the MEMS device110and the sound port180. The embedding arrangement may comprises the embedding material252and optionally also the cover layer170. The packaged MEMS device may further comprise the grille172within the sound port180.

FIG. 1may also be understood as schematically depicting a sound transducer component100that may comprise an embedding material252, a substrate-stripped MEMS die110, and a sound port180within the embedding material252. The substrate-stripped MEMS die110may be embedded within into the embedding material252and may comprise a diaphragm for sound transduction. The sound port180may be in fluidic and/or acoustic contact (fluidically and/or acoustically coupled) with the diaphragm. Hence, the sound port180may extend within the embedding material252as opposed to the substrate-stripped MEMS die being disposed directly at a surface of the embedding material252(i.e., the substrate-stripped MEMS die110being substantially flush with one of the exterior surfaces of the embedding material252). In other words, the substrate-stripped MEMS die110may be somewhat recessed with respect to said exterior surface of the embedding material.

The back cover190may also be called a cavity cover configured to cover the cavity160.

Silicon microphones or MEMS microphones typically need packaging to provide at least one of the following functionalities:mechanical protection of the MEMS partproviding an acoustical sound portproviding an acoustical reference volumehousing an ASIC for read-outEMI shieldingmechanical and electrical interconnect to the second level printed circuit board (PCB).

It is typically desired that the desired functions should be integrated in a minimum volume for advantageous application into, e.g., slim smartphones.

Regarding packing technologies for semiconductor devices a relatively new technology is “Wafer Level Packaging.” Compared to previous packaging technologies, wafer level packaging may provide advantages in flexibility (mostly in terms of the semiconductor manufacturing and/or packaging processes), cost, and performance. Wafer Level Packaging may be used to provide multi-die packages, i.e., packages comprising a plurality of (individual) dies. The individual dies may be similar or homogeneous to each other or they may be heterogeneous, such as a MEMS die and an ASIC as a second die. The ASIC may comprise electronic circuits that may be used for operating the MEMS die. In this manner, different dies produced by different, dedicated semiconductor manufacturing (e.g., a dedicated MEMS process comprising sacrificial material handling for the MEMS die, and e.g., a CMOS process for the ASIC) processes may be combined in a single package.

According to the wafer level package technology which are built on the silicon wafer, the interconnects may fit on the chip (so-called fan-in design). In a first step, dicing of a front-end-processed wafer may be performed and subsequently the singulated chips may be placed on a carrier. The chips can be placed on the carrier at a distance that can be chosen relatively freely. Typically the distance of the chips may be larger than the original distance of the chips on the original silicon wafer. A casting compound may now be used to fill the gaps and the edges around the chips in order to form the artificial wafer (reconstitution wafer). After curing, the artificial wafer may contain a mold frame around the dies and may be configured to carry additional interconnect elements, due to a “fan-out” that may result from placing the chips at a greater distance than they were originally present on the original silicon wafer. The term “reconstitution” refers to the built of the artificial wafer. Subsequent to the reconstitution, the chip pads can be electrically connected to the interconnects using, for example, thin-film technology.

While the possibility to increase the number of interconnects may be of particular interest for complex electronic semiconductor devices such as microprocessors, microcontrollers, analog-to-digital converters, digital-to-analog converters, etc. that typically require a large number of interconnects, the wafer level package technology may also provide new horizons for MEMS devices, such as sound transducers. When applying the package solutions according to wafer level package to MEMS sound transducers, it is possible to achieve a near chip scale integration, i.e., a small and thin volume of the packaged sound transducer component can be achieved. The cavity160that is needed in some sound transducer designs can be performed in an alternative manner and in some embodiments the cavity etch during front-end processing can even be omitted altogether. This avoids expensive etching technologies during the front-end-process, such as deep reactive ion etching processes (DRIE). The wafer level package solution proposed herein may also provide shielding, such as EMI shielding, as well as additional mechanical protection. In some embodiments to be described below, the wafer level package-based solution, or a part thereof, may even be a part of the sensor, i.e., of the sound transducing structure which, in the case of a capacitive sound transducer, typically comprises a diaphragm and a backplate (counter electrode).

The MEMS chip or MEMS die may be molded into the package and finally the back cavity may be realized by, e.g., wet chemical removal of the bulk silicon or at least a portion of the bulk silicon. As an additional aspect a (second) metallization layer may be used for EMI shielding of the critical interconnect between ASIC and the sensor (MEMS die). The (second) metallization layer can also be used for mechanical protection of the MEMS part (e.g., particle protection). Alternatively, the (second) metallization layer can also be used directly as a backplate (counter electrode).

In the following description some possible implementations are described with reference to the corresponding figures.FIGS. 2A to 2Hschematically illustrate a process flow according to an implementation with an oxide sacrificial layer.FIGS. 3A to 3Kschematically illustrate a process flow according to an implementation wherein a sound port is formed within a cover layer that is part of the package.FIGS. 4A to 4Gschematically illustrate a process flow for an implementation with a carbon sacrificial layer.FIGS. 5A to 5Fshow the possible implementations where the package or more precisely a component of the package is used as a functional part of the MEMS structure.

FIG. 2Ashows a schematic cross-section of a precursor MEMS die210as it may be output from a front-end-process and prior to a packaging process. The precursor MEMS die210comprises a substrate202and the actual MEMS structure which is disposed at a main surface of the substrate202. The substrate202and almost the entire MEMS structure may be separated from each other by an etch stop layer231which may be a silicon oxide, a silicon nitride, or may comprise a silicon oxide, a silicon nitride, or any other suitable material. At the surface of the substrate202, small islands216may be provided that are used during the formation of the corrugations116of the diaphragm112. The eventual gap113(seeFIG. 1) between the diaphragm112and the backplate114is still filled with a sacrificial material234such as an oxide, for example silicon oxide. The diaphragm112may further comprise a ventilation hole111for static pressure equalization as explained above. The sacrificial material234may also extend around the backplate114and within the holes211that are formed within the backplate. The sacrificial material234may be identical to the material of the etch stop layer231, but this is not necessarily so.

As to the electrical contacts it can now inFIG. 2Abe seen in more detail that, according to the depicted embodiment, contact117is configured to contact the substrate202, electrical contact119is configured to contact the diaphragm112, and contact115is configured to electrically contact the backplate114. Different arrangements of the electrical contacts115,117, and119are also possible.

The backplate114may comprise two layers: an electrically conductive layer215and a second layer214. The electrically conductive layer may comprise polysilicon, for example. The second layer214may comprise, for example, Si3N4, and may provide a base layer for polysilicon deposition and/or function as a diffusion barrier for the doping material of polysilicon (P-implantation). In addition or as an alternative, the second layer214may provide tensional stress, additional mechanical stability, and/or further electrical isolation.

The MEMS die210may further comprise a passivation layer232. The passivation layer232may be a SiON passivation with a thickness of approximately 400 nm, for example. In general, the passivation layer232may have a thickness for example in the range from about 200 nm to about 700 nm. The passivation layer232may cover the entire upper surface of the MEMS die210.

FIG. 2Bshows a schematic cross-section of the pre-packaging or precursor MEMS die210after an auxiliary layer242has been deposited on the passivation layer232. The auxiliary layer242has also undergone a planarization and a structuring so that the auxiliary layer242is present within a footprint area12of the sound transducing structure, only. Around the footprint area12the passivation layer232and the auxiliary structure242have been removed. Furthermore, also a margin of the sacrificial material234has been removed as far as it extended beyond the footprint area12. This removal may have been performed during the front-end-process and achieved by, for example, ion etching or another suitable semiconductor manufacturing technique. The backplate114and the layers232,242that are deposited on an upper surface of the backplate114are temporarily supported by the sacrificial material234, only. It is however possible to maintain at least a portion of a support structure such as a dielectric spacer between the diaphragm112and the backplate114at least at one or more positions along a circumference of the sound transducer structure/footprint area12. The auxiliary structure242may comprise phosphosilicate glass (PSG) and the thickness of the deposited auxiliary structure242may be between about 6 μm and about 30 μm, more specifically between 8 μm and 20 μm, for example about 12 μm. The deposition, planarization and structuring of the PSG layer242is however optional. The SiON passivation layer232alone would also do.

FIG. 2Cshows a schematic cross-section of the precursor MEMS die210having the deposited, planarized, and/or structured auxiliary structure242after it has been embedded into an embedding material252, for example by molding. While in the precedingFIG. 2Bthe precursor MEMS die210may typically be still provided on the original silicon wafer, along with a plurality of similar MEMS dies as output by the front-end-process, a chip singulation may have been performed betweenFIGS. 2B and 2C. According to at least some embodiments, a certain number of the precursor MEMS dies210may be arranged on a carrier having the size and the shape of a standard silicon wafer. The distance at which the individual MEMS dies210are placed may be larger than the distance at which they were spaced on the original silicon wafer so that a smaller number of the precursor MEMS dies210fits on an original wafer-sized carrier than are present on the original silicon wafer. The precursor MEMS dies210may be placed upside down on the carrier so that after embedding the MEMS dies210in the embedding material252a surface of the embedding material252is substantially flush with a surface of the auxiliary structure242. A thickness of the embedding material252may be selected to provide sufficient mechanical stability for the final sound transducer component100. InFIG. 2Cthe embedding material252may completely surround the substrate202of the precursor MEMS die210. In alternative embodiments, the embedding material252may be filled to a height so that a portion of the substrate202protrudes from a second main surface of the embedding material252(as mentioned above, the precursor MEMS dies210may be placed upside down on the carrier and the embedding material252may be poured onto the carrier to fill the gaps between the precursor MEMS dies210until the embedding material252has the desired height).

FIG. 2Dshows a schematic cross-section of the sound transducer component during the packaging process after a frontside redistribution layer (RDL)174has been formed. Furthermore, through contacts or vias122,124may have been formed in the embedding material252in order to electrically contact the contacts117and119of the MEMS die210. Although not shown inFIG. 2D, a further through contact or via may be provided for the contact115which may be used for electrically contacting the backplate114. The formation of the through contacts122,124and/or of the front side RDL174may be performed by laser drilling or by a another suitable method, such as a photolithography-based method.

FIG. 2Eshows a schematic cross-section after a further step of the packaging process has been performed. In particular, a cover layer170may have been deposited at the main surface of the embedding material252that may be substantially flush with the exposed surface of the auxiliary structure242. The cover layer170may comprise a LTC-imide (low temperature curing imide). As an alternative, the cover layer170may comprise a photoresist, for example SU-8. The cover layer170may be deposited in two steps wherein the first step covers the first redistribution layer174and provides an intermediate surface. Prior to the second step of the cover layer deposition, the second redistribution layer176may be deposited on said intermediate layer and subsequently structured. Furthermore, the grille172can also be created at this time. The grille172may be created at a surface of the embedded precursor MEMS die210, and in particular, as schematically illustrated inFIG. 2E, on a surface of the auxiliary structure242. Alternatively, the grille172may be created on a different surface as will be described below in the context of the description ofFIG. 3F.

The formation of the grille172may in particular comprise: a) depositing a seed layer on the auxiliary structure242(for example, by sputtering copper on to the surface of the auxiliary structure242—sputtered copper is typically unstructured and thus provides seed points for a subsequent copper deposition); b) applying a photoresist on the seed layer; c) exposing selected areas of the photoresist; d) developing the exposed photoresist so that the photoresist is removed at those positions where copper is to be grown on the seed layer; e) growing copper in the openings in the photoresist, e.g., by means of a deposition process; f) removing the remaining photoresist; and g) removing the copper seed layer. The height of the copper that can be grown in step e) is typically related to the thickness of the photoresist so that the height of the grown copper can be at most equal to about the thickness of the photoresist. The copper seed layer may be relatively thin so that it's removal does not significantly modify the grown copper structures forming the grille172since these structures are substantially thicker. As an alternative for copper, other suitable materials may be used, in particular metals. The grille172may be electrically conductive and may provide EMI shielding or, in embodiments to be described below, may function as a backplate in cooperation with the diaphragm112.

After the second redistribution layer176and the grille172have been formed, the second step of the deposition of the cover layer170may be performed. The embedding material252and the cover layer170may be regarded as an embedding arrangement.

FIG. 2Fshows a schematic cross-section after a further step of the method for packaging the MEMS die210has been performed. The (backside) cavity160may have been formed at a second main surface of the embedding material252by removing the substrate202of the embedded precursor MEMS die210, effectively resulting in a substrate-stripped MEMS die (or at least in a partially substrate-stripped MEMS die). The removal of the substrate or bulk silicon202may be done by a backside silicon etch step. In order to expose the substrate202which may be covered by a layer of the embedding material252, a grinding step may be performed at the second main surface of the embedding material252. Alternatively, said portion of the embedding material252that covers the substrate202may be removed by a chemical reaction, such as partially dissolving or etching away the embedding material252. Even though the MEMS die210may now be stripped of its substrate202or of a major part thereof, its individual components, in particular the diaphragm112and the backplate114, may be still in a well defined spatial relation to each other. First of all, the sacrificial material234may still be present between the diaphragm112and the backplate114. Moreover, the embedding material252may brace the remaining parts of the initial precursor MEMS die210, namely the diaphragm112and the backplate114.

FIG. 2Gshows a schematic cross-section after the auxiliary structure242between the passivation layer232and the grille172may have been removed. In this manner, an auxiliary portion (e.g., the auxiliary structure242) of the embedded precursor MEMS die210adjacent to the grille172may be removed to create the sound port180within the embedding arrangement252,170. The removal of the auxiliary structure242(e.g., phosphosilicate glass, PSG) may comprise an etching step from the front side. After the removal of the auxiliary structure242, the sound port180or a portion of the sound port180may be obtained. As a result, the grille172may be disposed in the sound port180or across the sound port180.

FIG. 2Hshows a schematic cross-section after a release etch may have been performed and after backside coverage. By performing the release etch, the sacrificial layer/material234may have been removed between the diaphragm112and the backplate114so that the gap113may be created. InFIG. 2Hthe backside cavity160may be closed by a backside cover190. Backside cover190may be a plastic film, an injection molded part that is attached to the mold compound while injection molding the backside cover190, a small piece of metal, or even a wall of a housing of the system/application layer (e.g., smartphone, tablet PC, digital camera, etc.) in which the sound transducer component100is used. The order of the process steps schematically illustrated inFIGS. 2A to 2Hmay be changed. For example, backside coverage may be performed earlier, e.g., prior to the removal of the auxiliary structure242.

As mentioned in the previous paragraph, the final sound transducer component (packaged MEMS device)100as schematically illustrated inFIG. 1may be obtained after the passivation layer232and the sacrificial material234have been removed by suitable etching steps performed from the front side of the sound transducer component100, i.e., through the openings of the grille172. The sacrificial material234may comprise TEOS (tetraethyl orthosilicate). The mechanical stability of the MEMS part comprising the diaphragm112and the backplate114may now be provided mainly by the embedding material252. As can be seen inFIG. 2H, the packaged MEMS device100may comprise the MEMS device (comprising primarily the diaphragm112, the backplate114, and possibly some remainders of a support structure) which is disposed between the sound port180and the backside cavity160. The packaged MEMS device100may further comprise the embedding arrangement (comprising primarily the embedding material252and the cover layer170), the grille172which may be disposed in or across the sound port180, and the backside cover190.

The described packaging process is believed to have significant potential for reducing the fabrication cost of a sound transducer component because the backside cavity160can be formed in a cost-efficient manner, for example by wet etching the substrate202of the original MEMS die210. Expensive etching technologies such as DRIE are not necessary anymore. In contrast, other methods for fabricating and packaging a sound transducer component that do not provide for etching away the substrate202after the MEMS die210has been embedded by molding into the embedding material252may be constrained to create the cavity160during the front-end-process, either by DRIE or by a chemical etching step. Note that chemical etching in silicon can typically leads to diagonal or tapered sidewalls (approximately 54°) which means that the cavity160would need a much larger footprint area. This increases the required area for the MEMS die on the original silicon wafer, which in turn leads to more “wasted” silicon area. In other words, reducing the amount of wasted area on the original silicon wafer has a great potential regarding cost efficiency and wafer yield.

FIGS. 3A to 3Kschematically illustrate a process flow using a sequence of schematic cross sections for an implementation example that avoids the auxiliary material242and instead uses a first partial layer of the cover layer170as a basis for depositing and structuring the material for forming the grille172.

FIG. 3Bshows a schematic cross-section of the precursor MEMS die210after the passivation layer232may have been structured in order to expose portions of the backplate114and of the diaphragm112. In this manner, the embedding material252may come into contact with said portions of the backplate114and of the backplate112in order to eventually function as a support structure for the backplate114and the diaphragm112. The passivation layer232may be structured by an anisotropic etching process, such as reactive ion etching (RIE). The difference to the implementation example shown inFIG. 2Bis that in the implementation example ofFIG. 3Bno auxiliary structure242is used. The passivation layer232may be planarized.

FIG. 3Cshows a schematic cross-section of the MEMS die210after it has been embedded by molding into a embedding material252. The surface of the passivation layer232may be substantially aligned or flush with the surface of the embedding material252.

FIG. 3Dshows a schematic cross-section of the sound transducer component during the packaging process after a frontside redistribution layer (RDL)174may have been formed. Furthermore, through contacts or vias122,124may have been formed in the embedding material252in order to electrically contact the contacts117and119of the MEMS die210.

FIG. 3Eshows a schematic cross-section of the embedded precursor MEMS die after a further step of the packaging process may have been performed. In particular, a first portion of a cover layer170may have been deposited at the main surface of the embedding material252that is substantially flush with the exposed surface of the passivation layer232. The first portion of the cover layer170may cover the first redistribution layer174and may provide an intermediate surface of the embedding precursor MEMS die. The first portion of the cover layer170may comprise imide, LTC-imide, and/or SU-8.

FIG. 3Fshows a schematic cross-section after a second redistribution layer176and a grille172have been formed at the intermediate surface. In this manner, the second redistribution layer176and the grille172may be provided in a common plane. In particular, there is no step between the grille172and the second redistribution layer176as in the implementation example shown inFIG. 2E. The absence of the step between the grille172and the second redistribution layer176may be beneficial in terms of easier manufacturing.

InFIG. 3Ga portion of the cover layer170located between the grille172and the passivation layer232may have been removed to create the sound port180. Said portion of the cover layer170may be removed by introducing an etching agent, a solvent, or an oxidant through the openings of the grille172. In other words, an auxiliary portion of the embedded precursor MEMS die adjacent to the grille172may be removed.

FIG. 3Hshows a schematic cross-section after a second layer of the cover layer170has been provided that covers the second redistribution layer170, for example by a deposition process. The area of the grille172and of the contact pad178may be omitted from covering with the second layer of the cover layer170. In the alternative, the cover layer170may be structured after deposition, in order to expose the grille172and the contact pad178. It may also be possible to perform the step corresponding toFIG. 3Hprior toFIG. 3Gso that the cover layer170is first completed (i.e., deposition and structuring) before creating the sound port180.

InFIG. 3Ia portion of the embedding material252may have been removed at a side opposite to the cover layer170so that the substrate202of the MEMS die210may be exposed.

FIG. 3Jshows a schematic cross section of the packaging process of the MEMS die210after the substrate202of the MEMS die210has been removed. In this manner, the backside cavity160may be created. The removal of the substrate202may comprise an etching step which may stop at the etch stop layer231.

FIG. 3Kschematically shows the result of the release etch by which the sacrificial material234may be removed between the diaphragm112and the backplate114to provide the gap313. Concurrently, the etch stop layer231may be removed, if the same material or a similar material is used for the etch stop layer231and for the sacrificial material234.

FIG. 3Lshows the finished sound transducer component comprising a back cover190to close the cavity160. In other words,FIG. 3Lshows a schematic cross section of a packaged MEMS device comprising a MEMS device, a sound port180adjacent to the MEMS device, an embedding arrangement252,170that encapsulates the MEMS device and the sound port180, and a grille172within the sound port. As shown inFIG. 3L, the MEMS die may be recessed with respect to a first main surface of the embedding material252, i.e., the surface that interfaces with the cover layer170. The recess may be caused by the passivation layer232that was originally present at the precursor MEMS die and subsequently removed to provide an acoustic and/or fluidic access from the exterior to the backplate114and the diaphragm112. The grille170may be disposed in or across the sound port180.

FIGS. 4A to 4Gschematically illustrate a process flow using a sequence of schematic cross sections for the implementation example that may use a carbon sacrificial layer434instead of the TEOS sacrificial layer234. According to the implementation example presented inFIGS. 4A to 4G, the passivation layer232and the auxiliary structure242in the example according toFIGS. 2A to 2Hmay also be made of carbon, i.e., the sacrificial layer and optionally the protective cover layer are made from carbon.FIG. 4Ashows a schematic cross-section of the precursor MEMS die410as it may be output by the front-end-process and possibly before singulating. The carbon layer434may fill the spaces that will eventually be transformed into the gap113between the MEMS diaphragm112and the backplate114and also the space that will eventually be occupied by (a portion of) the sound port180. The carbon sacrificial layer434may furthermore fill the perforation holes that are formed in the backplate114. The carbon sacrificial layer434may be formed in several phases which may be separated by a deposition and structuring of another material, such as the material for the backplate114.

FIG. 4Bshows a schematic cross-section after chip singulation and embedding the precursor MEMS die410into the embedding material252. A portion of the passivation layer232or of the support structure of the precursor MEMS die410may still be present and may also be embedded into the embedding material252.

FIG. 4Cshows a schematic cross-section of the semi-finished sound transducer component after a process step to form a front side redistribution layer has been performed at a first main surface of the embedding material252. This method step may involve via-laser and a first copper layer (first CU)174.

FIG. 4Dshows a schematic cross-section after a second front side RDL has been performed. In a larger sense, the second front side RDL may comprise the deposition or formation of a first layer of the cover layer170(e.g., LTC-imide), a second copper layer176and a further layer of the cover layer170(e.g., LTC-imide). The grille172may be formed as described above. Once this step has been performed, the structure as schematically illustrated as a cross-section view inFIG. 4Eis obtained. The substrate202and also the etch stop oxide231(see, for example,FIG. 4A) may be removed so that the backside cavity160has been created.

FIG. 4Fshows a schematic cross-section after a backside coverage has been done using a backside cover190.

FIG. 4Gshows a schematic cross section after the method steps of fast dry release etch of the protection layer and sacrificial layer carbon434by oxide plasma etch. According to alternative embodiments, the release etch can be done prior to backside coverage, especially in the case of bottom backplate microphones or double backplate microphones, as the gap113between the diaphragm112and the backplate electrode114is more easily accessible through the backplate114, due to the perforation of the backplate114.

InFIGS. 5A to 5Fto be described next, a possible implementation example is presented where the package serves as a part of the MEMS.FIG. 5Ashows a schematic cross-section of a precursor MEMS die510as it may be present on the original silicon wafer output by the front-end wafer process. The precursor MEMS die510may comprise the substrate202, the etch stop layer231, a remaining portion of a passivation layer232, the membrane112, and the sacrificial layer534. Accordingly, the silicon die510may comprise only the membrane layer112plus the sacrificial layer534on top, but not a backplate layer. The sacrificial layer534may be TEOS or carbon or any other suitable sacrificial material.

FIG. 5Bshows a schematic cross-section after the preliminary MEMS die510has been embedded by molding into the embedding material252. Furthermore, a front side RDL (1) may have been done using via-laser and a first copper layer174.

FIG. 5Cshows a schematic cross-section where a second front side RDL step may have been performed including forming a first LTC-imide layer, a second copper layer176and a second LTC-imide layer. The cover layer170may thus comprise the LTC-imide layers and the first and second copper layers174,176. An electrically conductive grille172may also be formed or created at an exposed surface of the sacrificial layer534.

FIG. 5Dshows a schematic cross-section after grinding, silicon etching, and stop oxide etching at a backside of the semi-finished sound transducer component. In this manner, the backside cavity160may be formed in the space originally occupied by the substrate202of the MEMS die510.

In the schematic cross section ofFIG. 5Ethe backside cavity160may have been covered by the backside cover190.

After the fast dry release etch of the protection layer and sacrificial layer carbon534by oxide plasma etch, the structure schematically illustrated in the cross-section ofFIG. 5Fmay be obtained. The removal of the protection layer and sacrificial layer carbon534may leave the gap513between the diaphragm112and the grille172which may now serve as the perforated backplate or counterelectrode of the MEMS transducer. As already mentioned before, the release etch can be done prior to backside coverage (FIG. 5E). The schematic cross-section inFIG. 5Fsubstantially shows the finished sound transducer component500.

The sound transducer component500may comprise the perforated backplate172generated by the second redistribution layer (RDL (2)). The air gap513may be controlled by carbon/oxide layer thickness. The silicon membrane or diaphragm112may be relatively well controlled by the front-end-process. Depending on the intended application of the sound transducer component, the air gap513and the perforated backplate172might not require as high a precision as the silicon diaphragm112and may therefore also be produced during the back-end-of-line processing or the packaging.

According to further implementation examples, the MEMS die110,210,410,510may comprise a spacer234,334,434,534that may be arranged at an opposite side of the diaphragm112than the cavity160. The spacer may be at least partially embedded in the embedding material252during the step of embedding the MEMS die in the embedding material. The method may further comprise forming the grille172on a surface of the spacer234,334,434,534.

The method may further comprise removing the spacer234,334,434to form a transducer opening (sound port)180extending to the diaphragm112within the embedding material252.

The method may further comprise a step of forming a first cover layer at a first surface of the embedding material252. The first cover layer may comprise a (first) redistribution layer174. The redistribution layer174may be configured to provide electrical contact for the MEMS die110.

The method may further comprise embedding by molding a further die such as an ASIC into the embedding material252. The redistribution layer(s)174,176may be configured to provide an electrical connection between the MEMS die110and the further die, e.g., the ASIC.

The method may further comprise forming a second redistribution layer176within the cover layer170. The second redistribution layer176may provide electromagnetic interference (EMI) shielding for the (first) redistribution layer(s)174.

According to a further implementation example a sound transducer component may comprise an embedding material252, a substrate-stripped MEMS die110embedded by molding into the embedding material252, a cavity160, and a transducer opening (sound port)180. The MEMS die may comprise a diaphragm112for sound transduction. The cavity160may be formed within the embedding material252and maybe in (fluidic or acoustic) contact with the diaphragm112. The transducer opening180may be formed within the embedding material252and may be in (fluidic or acoustic) contact with the diaphragm112at an opposite side of the diaphragm112than the cavity160.

A further possible example of implementation is provided by a method for packaging a MEMS die of a sound transducer component. The method may comprise forming or creating a plurality of spacers234,334,434, or534at a surface of a wafer comprising a plurality of precursor MEMS dies (e.g., precursor MEMS dies)210,410,510. Each spacer may cover at least a portion of a diaphragm of a corresponding MEMS die. The method may further comprise singulating wafer to obtain a plurality of singulated semi-finished precursor MEMS dies. A selected number of the plurality of singulated precursor MEMS dies may then be embedded by molding in an embedding arrangement comprising an embedding material252to form a reconstitution wafer. The singulated precursor MEMS dies may be embedded together with their corresponding spacers. The method may also comprise removing at least a portion of the plurality of spacers to obtain a plurality of sound ports180within the embedding arrangement252. The reconstitution wafer may then be singulated to thereby form the sound transducer component. A spacer may be or comprise the auxiliary structure242,434, or534. In the alternative or in addition, a spacer may be or comprise a portion of the passivation layer232, and/or a portion of the cover layer170.

Although each claim only refers back to one single claim, the disclosure also covers any conceivable combination of claims.