Semiconductor device and method for manufacturing a semiconductor device

Abstract

Embodiments of the present disclosure relate to semiconductor devices and methods for manufacturing semiconductor devices. A semiconductor device includes a substrate, a transduction microstructure integrated into the substrate, a cap bonded to the substrate and having a first surface adjacent to the substrate and a second external surface, and a channel extending through the cap from the second surface to the first and in communication with the transduction microstructure. A protective film of porous polysilicon microstructures permeable to gaseous substances is disposed across the channel.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a semiconductor device and to a method for manufacturing a semiconductor device. BACKGROUND

[0002] It is well known that electronic, microelectromechanical and microfluidic devices must be protected from the effects of external agents, such as dust, humidity and aggressive substances, which can cause malfunctions and damages. In many cases, the devices can be sealed inside a package which, from a mechanical and fluidic point of view, completely isolates the device from the external environment, while enabling electronic or electromagnetic coupling. However, there are devices, in particular some transducers, which by their nature not only need to be electrically connected to the external world but also cannot therefore benefit from a sealed package. For example, depending on the type and operating principle of the device, electroacoustic transducers (microphones and loudspeakers), pressure sensors and sensors for detecting gases or volatile substances must be fluidically coupled to the environment for receiving and transmitting static pressure or pressure variations. The packaging of these devices is therefore provided with openings which, on the one hand, guarantee correct operation and, on the other hand, reduce the risk of penetration of potentially harmful external agents. Examples of other devices which cannot be sealed are some types of actuators and various microfluidic circuits and devices, such as micro-pumps or microfluidic valves.

[0003] The known solutions envisage closing the openings by applying a layer of breathable polymer fabric (e.g. expanded polytetrafluoroethylene, ePTFT) or providing the openings in the form of channels or vents with a very small cross-section so as to prevent the entry of particles and dust above a given diameter. However, both solutions have limitations, in the first case the application of the fabric layer requires very high costs since the operations can only be performed by pick-and-place on individual devices and cannot be performed during the machining at wafer level. The channels or vents can be provided during the manufacturing at wafer level, however, given that the package usually has an appreciable thickness in order to provide adequate mechanical protection, it can be difficult to reduce the diameter of the channels until the required protection is guaranteed. Therefore, fine particles can reach the devices to be protected. SUMMARY

[0004] The present disclosure aims to provide a semiconductor device and a method for manufacturing a semiconductor device which overcome or at least attenuate the limitations described above.

[0005] The present disclosure relates to a device comprising a transducing microstructure on a substrate. There is a cover coupled to the substrate and having a first face facing the substrate and an external second face. A channel extends through the cover from the second face to the first face and is in fluid communication with the transducing microstructure. The channel comprises internal side walls. A protective film of porous polysilicon spans the channel and is located on the internal side walls of the channel. BRIEF DESCRIPTION OF DRAWINGS

[0006] For a better understanding of the present disclosure, some embodiments thereof will now be described, by way of non-limiting examples only, and with reference to the appended drawings, wherein:

[0007] Figure 1 A cross-sectional view of a semiconductor device according to an embodiment of the present disclosure is shown;

[0008] Figure 2 An enlarged detail of the device of Figure 1 is shown;

[0009] Figure 3 Cross-sectional views through a semiconductor device according to different embodiments of the present disclosure are shown;

[0010] Figure 4 A cross-sectional view of a semiconductor device according to another embodiment of the present disclosure is shown;

[0011] Figures 5 to 14 A semiconductor wafer in successive processing steps of a process for manufacturing a semiconductor device according to another embodiment of the present disclosure is shown;

[0012] Figure 15 A cross-sectional view of a semiconductor device according to another embodiment of the present disclosure is shown;

[0013] Figures 16 to 19 A semiconductor wafer in successive processing steps of a process for manufacturing a semiconductor device according to different embodiments of the present disclosure is shown; and

[0014] Figure 20 A simplified block diagram of an electronic system including a semiconductor device according to the present disclosure is shown. DETAILED DESCRIPTION

[0015] Reference is made to Figure 1A semiconductor device according to an embodiment of the present disclosure, in particular a transducer indicated by the numeral 1, comprises a substrate 2, a transducing microstructure 3 integrated in the substrate 2, and a cap 5. In the example illustrated, the transducer 1 is a pressure sensor, and the transducing microstructure 3 comprises an elastic transducing membrane 6 closing a chamber 7 on one side. In other embodiments not illustrated, the semiconductor device can be a different type of transducer, such as, by way of non-limiting example, an electroacoustic transducer (microphone or loudspeaker) or a sensor for detecting a gas or a volatile substance; an actuator; a microfluidic device, comprising a microfluidic circuit and possibly microfluidic components, such as a micropump and possibly a microfluidic valve. For example, the semiconductor device can be a so-called "lab-on-a-chip", which requires at least one inlet for introducing a biological sample or a reagent to be analyzed from the outside to the microfluidic circuit. Moreover, it is understood that the transducing microstructure does not necessarily comprise movable or deformable parts. For example, the transducing microstructure in a volatile substance sensor can comprise a region having a fixed geometry obtained using a material having electrical properties that depend on the concentration of the material under study.

[0016] The face of the transducing membrane 6 with respect to the chamber 7 can be free or coated with a passivation layer 8 and communicates with the external environment, as will be illustrated in detail hereinafter. The thickness and the rigidity of the passivation layer 8 are in any case chosen so as to enable the deformation of the transducing membrane 6 as a result of the pressure variations in the detection range.

[0017] In one embodiment, the transducing microstructure 3 is connected to the rest of the substrate 2 by means of elastic suspension elements 10.

[0018] The cap 5 comprises a bulk 4 of semiconductor material (for example, single-crystal silicon) and has a first face 5a adjacent to the substrate 2, which is bonded to the substrate 2, and a second face 5b facing outwards. The cap 5 has a thickness so as to provide, for example, mechanical protection to the transducing microstructure 3 and has a thickness in the first direction comprised, for example, between 100 μιη and 700 μιη.

[0019] A pedestal or extension 11 extends from the first face 5a of the cap 5, which is coated inside with a respective coupling coating 12 (for example, made of germanium), and the pedestal 11 is bonded to a respective bonding pad 13 of the substrate 2. The pedestal 11 has a height with respect to the first face 5a of the cap 5 so as to create a gap 14 between the cap 5 (in particular, the first face 5a) and the substrate 2. For example, the height of the pedestal 11 in the first direction can be comprised between 1 μιη and 10 μιη. The transducing microstructure 3 and the gap 14 communicate.

[0020] In Figure 1In an embodiment, the channel 15 extends from the second face 5b through the cover 5 to the first face 5a. The channel 15 thus has a first end portion which opens outwards and a second end portion which communicates with the gap 14 and the transduction microstructure 3. The channel 15 has a diameter in the second direction transverse to the first direction, which diameter is chosen according to design preferences and for example comprises between 10 pm and 30 pm.

[0021] As shown in more detail in Figure 2 , the cover 5 comprises a protective film 17 made of porous polysilicon and permeable to gaseous substances, which is arranged so as to be disposed across the channel 15. It can be understood that the protective film 17 can be positioned at the first end of the channel 15 on the second surface 5b of the cover 5, or at the second end of the channel 15 on the first face 5a of the cover 5, or positioned along the channel 15 at an intermediate position between the first end and the second end. In particular, the protective film 17 is part of a porous polysilicon region 18 which extends from the first face 5a of the cover 5 towards the inside of the channel 15, and which coats the lateral surface of the channel 15 itself between the first face 5a and the protective film 17. In an embodiment, the protective film 17 is released on both sides.

[0022] The porosity of the protective film 17 is chosen so as to inhibit passage of particulate solid materials, dust, and to enable passage of gaseous substances. In an embodiment, the pores 19 Figure 2 of the polysilicon forming the protective film 17 can have an equivalent diameter comprised between 5 nm and 50 nm. By "equivalent diameter" we mean here the diameter of a dust having a circular or circular channel section and a pipe equal to the area of the average channel section of the pores. The pores 19, represented in Figure 2 for simplicity as straight channels having a constant section, actually extend along a general curve having a variable cross-section. Furthermore, the size and density of the pores 19 of the protective film 17 are such that the empty / full ratio is between 5% and 30%. With these characteristics, the protective film 17 is able to retain water in drops. In fact, as a result of surface tension, the water drops cannot penetrate the pores 19 without a pressure difference being applied on both sides of the protective film 17. The channel 15 is offset with respect to the centre of the membrane 6.

[0023] With reference to Figure 3In an embodiment of the packaged semiconductor sensor indicated by 100, a plurality of channels 115 are included, extending through a cover 105 from a second surface 105b to a first surface 105a. Each channel 115 is provided with a corresponding protective film 117 made of porous polycrystalline silicon. The protective film 117 is part of a region 118 of the porous polycrystalline silicon and is permeable to gaseous substances. The region 118 of the porous polycrystalline silicon extends from the second surface 105b of the cover 105 toward the interior of the corresponding channel 115 and is coated on the side surface of the channel 115 itself between the second surface 105b and the protective film 117. The number, size, and location of the channels 115 are determined based on design preferences.

[0024] Multiple channels 115 are located between pedestals 11. Channels 115 are spaced equally from adjacent channels. The first channel, closer to the first pedestal 11, is aligned with the first side of the membrane 6. A second channel is arranged to cover the membrane 6. A third channel is on the second side of the membrane. The second channel is located between the first and third channels. Figure 4 In the embodiment shown, in the packaged semiconductor transducer 200, a protective film 217 forms part of a polysilicon region 218 that extends from the second outer surface 205b of the cover 205 toward the interior of the channel 215 and is coated on the side surface of the channel 215 itself between the second surface 205b and the protective film 217. The film 217 includes a portion on the second surface 205b and a portion of the side surface or interior sidewall of the channel 215. A portion of the side surface extends partially into the channel, such that more sidewalls are not covered by the film covering a portion of the side surface 217.

[0025] The membrane 217 is on the second surface 205b and the pedestal is on the first surface 205a, with the membrane and the pedestal facing each other.

[0026] Figure 1 The packaging of semiconductor transducer 1 can be referenced. Figures 5 to 13 The described method was manufactured.

[0027] The transducer microstructure 3 was obtained using a microstructured semiconductor wafer 2′ according to known methods (in... Figure 14 (See in the middle).

[0028] In order to manufacture Figure 1 The cover 5, comprising the monocrystalline silicon body layer 4′ of the cover semiconductor wafer 5′, is etched by a first resistive structure 20a defined by a first mask 20b, as shown in the image. Figure 5 As shown in the diagram, the body layer 4′ has its thickness removed corresponding to the height of the pedestal 11, which is formed in the region protected by the first mask 20. The height is from surface 5a to the outermost surface of the pedestal.

[0029] The semiconductor wafer 5' is then dry-etched using a second resist structure 21a (defined using a second mask 21b) to open trenches 23, as shown. Figure 6 As shown. In the examples illustrated in this article, anisotropic dry etching is used, but wet etching can be used equally, depending on design preference.

[0030] Then( Figure 7 On the cap semiconductor wafer 5′, a porous polycrystalline silicon barrier layer 24 and a protective layer 25 are successively formed on the first surface 5a and within the trench 23, and the barrier layer 24 and the protective layer 25 are permeable to gaseous substances. The barrier layer 24 may be a thermally deposited or grown silicon oxide layer. Alternatively, different materials that can be selectively etched for polycrystalline silicon, such as multilayer silicon oxide and silicon nitride, may be used. The protective layer 25 is deposited on the barrier layer 24 and may have a thickness including between 80 nm and 150 nm. Furthermore, the diameter of the holes and the empty / fill ratio of the protective silicon layer 25 are selected based on the design preferences of the protective film 17 described above. For example, the protective layer 25 has holes with an equivalent diameter including between 5 nm and 50 nm. The size and density of the holes result in an empty / fill ratio including between 5% and 30%.

[0031] The stop layer 24 and the protective layer 25 cover the first surface 5a of the semiconductor wafer 5', the sidewalls of the trench 23, and the bottom in a consistent manner. The protective layer 25 forms a protective film 17 on the bottom of the trench 23.

[0032] After the stop layer 24 and the protective layer 25 have been formed, the resist structure 26a is deposited and defined via a third mask 26b to protect the interior of the trench 23, such as... Figure 8 As shown. The stop layer 24 and the protective layer 25 are not composed of a third resist structure 26a. Figure 9 The protected area is selectively etched. A porous polycrystalline silicon region 18 is thus obtained, which is separated from the body monocrystalline silicon layer of the cover semiconductor wafer 5' by a stop structure 24' defined by the remainder of the stop layer 24.

[0033] After the third resist structure 26a has been removed, the coupling layer 28 (e.g., germanium) is deposited on the semiconductor wafer 5′ in a consistent manner. Figure 10 ).

[0034] The fourth resist structure is then transmitted through the fourth mask 29b ( Figure 11 The fourth resist structure 29a is deposited and defined. It coats the base 11 and the coupling layer 28 surrounding it. The coupling layer 28, not protected by the fourth resist structure, is selectively etched and removed. The coupling coating 12 is thus created, as... Figure 12 As shown.

[0035] With reference to Figure 13 , the cover semiconductor wafer 5' is flipped over in a position corresponding (i.e. aligned) to the trenches 23 and etched on the back using a significantly anisotropic etch (e.g. etching trenches) until reaching the stop structure 24', which protects the porous silicon region 18 in this step. The channel 15 is thus completed. The stop structure 24' is in turn selectively etched. In particular, the portion of the stop structure 24' exposed within the channel 15 is removed, thus releasing the protective film 17. The protective film 17 thus extends in a direction transversal to the longitudinal axis of the channel 15. The portions of the channel 15 on opposite sides of the protective film 17 are in communication with each other through the protective film 17 of porous polysilicon.

[0036] The cover semiconductor wafer 5' is finally bonded to the bonding pads of the microstructure semiconductor wafer 2' to form a composite wafer Figure 14 , which is cut, thus obtaining Figure 1 a plurality of examples of packages of semiconductor transducers. Each example comprises a portion of the microstructure semiconductor wafer 2' which defines the base 2 and comprises the transducing microstructure 3, and a portion of the cover semiconductor wafer 5' which defines the cover 5.

[0037] To generate Figure 3 the packaged semiconductor transducer 100, the method can be immediately modified by modifying the masks 21 and 26, and the etching of the trenches on the back side of the cover semiconductor wafer, so that the desired number of channels is opened, instead of just one.

[0038] To manufacture Figure 4 the packaged semiconductor transducer 100, after the seat 11 has been formed, the packaged semiconductor wafer is flipped over. The processing operations are carried out on the back of the cover semiconductor wafer (second face 205b), as already described, until the stop layer 24 and the protective silicon layer 25 are etched to form the polysilicon region 218 and the stop structure 24'. Before depositing the germanium coupling layer, the wafer is flipped over again. The processing operations continue with the formation and definition of the coupling layer on the first face 205a of the cover semiconductor wafer, and with the anisotropic etching of the bulk layer to form the channel 215, followed by the selective removal of the stop layer within the channel 215. The cover semiconductor wafer is bonded to the microstructure of the semiconductor wafer 2' and, after the individual cutting of the deposited wafer thus obtained, Figure 4 an example of the packaged semiconductor transducer 200 is obtained.

[0039] With reference to Figure 15 , the packaged semiconductor transducer is indicated by the number 300 according to an embodiment of the present disclosure, and it comprises a base 2, in which a transducing microstructure 3 is integrated.

[0040] The cap 305 includes a main layer 324, a stop layer 324, a structural layer 341, and a protective layer 325 supported by porous polycrystalline silicon and permeable to gaseous substances. The silicon oxide stop layer 324 is interposed between the main layer 304 and the structural layer 341. The main layer has monocrystalline silicon, and the structural layer 341 is made of a selectively etchable material, such as silicon nitride.

[0041] Channel 315 extends from the second surface 305b of the cover through the main body layer 304, the stop layer 324, and the structural layer 341 to the first surface 305a. A protective layer 325 forms a protective film 317 within the channel 315. More precisely, the protective layer 325 (covering the first surface 305a of the cover 305) penetrates into the channel 315, substantially coating the side surfaces of the channel 315 up to the interface 343 between the structural layer 341 and the stop layer 324. At the depth of the interface 343, the protective layer 325 extends in a direction transverse to the longitudinal axis of the channel 315 to form the protective film 317.

[0042] The first surface 305a of the cover 305 is joined to the base 2 by a pedestal 311, which serves as an adhesive structure and also has height to create a gap 314 between the base 2 and the cover 305.

[0043] The microstructure 3 is connected to the outside through channel 315 and a protective membrane 317 that allows gaseous substances to pass through.

[0044] According to the manufacturing Figure 15 Methods for packaging semiconductor transducers in Figures 16-19 As shown, the transducer microstructure is obtained using a microstructured semiconductor wafer 2′ as already described, and the cap semiconductor wafer 305′ initially includes a body layer 304. A stop layer 324 and a structural layer 341 are sequentially formed on the body layer 304. Figure 16 )superior.

[0045] The structural layer 341 is then selectively etched using a mask 320 to open the cavity 345, which extends to the stop layer 324, as shown. Figure 17 As shown.

[0046] A protective layer 325 is then formed on the cover semiconductor wafer 305'. Figure 18 On the first surface, the cover semiconductor wafer 305′ is then flipped over, and on the back side, i.e., on the side of the second surface 305b, in accordance with (aligned with) the corresponding cavity 345. Figure 19 The etching is performed at the location of the stop layer 324. In particular, significantly anisotropic trench etching is first performed up to the stop layer 324, and then the stop layer 324 is etched at its exposed location. In this way, the protective film 317 is released and the channel 315 is completed.

[0047] The protective layer 325 is selectively etched to expose the structure layer 341, whereupon the mesa 311 is formed.

[0048] The cover semiconductor wafer 305' is finally bonded to the bonding pads of the microstructure semiconductor wafer to form a composite wafer, which is in turn diced, thus obtaining a plurality of packaged semiconductor transducers Figure 15 A plurality of examples of packaged semiconductor transducers are shown. Each example comprises a portion of a microstructure semiconductor wafer 2' defining a base 2 and comprising a transducing microstructure 3, and a portion of a cover semiconductor wafer 305' defining a cover 305.

[0049] The described disclosure presents various advantages. From a structural point of view, the presence of the protective membrane across one or more channels prevents any contamination of the transducing microstructure by particles and dust within the device, without jeopardizing the fluidic connection with the outside world, in particular for gaseous substances. Moreover, the protective membrane prevents or at least hinders the entry of small amounts of liquid, for example due to exposure to splashes or to use during sports activities. For example, in the case of water, the diameter of the holes of the protective membrane is sufficient to prevent the entry of droplets due to surface tension.

[0050] Thanks to the transducing microstructure, the proper operation of the transducer is ensured, despite remaining protected from contaminants, in any case retaining and coupling to the quantity to be detected (pressure, substance, etc.) thanks to the porosity of the protective membrane. In fact, the limit on the minimum diameter of the channels can even be relaxed at least in part, since the barrier effect against contaminants is effectively performed by the protective membrane. The presence of the protective membrane therefore also provides greater flexibility in the design of the cover.

[0051] As regards the manufacturing method, the use of a stop layer between the porous polysilicon and the bulk layer enables the definition and release of the protective membrane within the channels in a simple manner during wafer-level mechanical processing. The operations for applying a polymeric membrane on the device level after separation can be avoided, with a consequent reduction in the considerable costs. Moreover, the stop layer and the porous polysilicon layer can be formed using standard techniques of mechanical processing of semiconductors, thus in a reliable and inexpensive manner. Other characteristics of the protective membrane, such as porosity and thickness, are easily controlled.

[0052] The bulk layer is etched on both sides, before opening the trench on one side and then anisotropic etching on the opposite side, enabling the shape ratio of the extremities of the channel crossing the cover to be obtained. Moreover, the channel can be formed without any need to thin the cover wafer and thus without reducing its mechanical resistance. This increases the flexibility in designing and manufacturing the semiconductor transducer.

[0053] Figure 20An electronic system 400, which can be of any type, in particular, but not exclusively, a wearable device, for example, a watch, a bracelet or a smartband, a computer, such as a mainframe, a personal computer, a notebook or a tablet computer; a smartphone; a digital music player, a digital camera or any other device designed to process, store, send or receive information, is shown. The electronic device 1 can be a general purpose or embedded processing system in a device, an apparatus or other system.

[0054] The electronic system 400 comprises a processing unit 402, a memory device 403, a packaged semiconductor sensor, for example, the packaged semiconductor sensor 1 of Figure 1 The electronic system 400 can also be equipped with input / output (I / O) devices 405 (for example, a keyboard, a mouse or a touch screen), a wireless interface 406, peripheral devices 407.1,..., 407.N and possibly other auxiliary devices (not shown here). The components of the electronic system 400 can be communicatively coupled to each other directly and / or indirectly through a bus 408. The electronic system 400 can also comprise a battery 409. It should be noted that the scope of the present disclosure is not limited to embodiments that must have one or all of the listed devices.

[0055] The processing unit 402 may, for example, comprise one or more microprocessors, microcontrollers or the like, according to design preferences.

[0056] The memory device 403 can comprise various volatile and non-volatile memory devices, for example, SRAM and / or DRAM for volatile and solid-state memory, magnetic and / or optical disks for non-volatile memory.

[0057] Finally, it is clear that modifications and changes can be made to the described devices and methods without departing from the scope of the present disclosure.

[0058] A semiconductor device can be summarized as comprising: a substrate (2); a transducing microstructure (3) integrated on the substrate (2); a cap (5; 105; 205; 305) bonded to the substrate (2) and having a first face (5a; 105a; 205a; 305a) adjacent to the substrate (2) and an external second face (5b; 105b; 205b; 305b); a passage (15; 115; 315) extending through the cap (5; 105; 205; 305) from the second face (5b; 105b; 205b; 305b) to the first face (5a; 105a; 205a; 305a) and in communication with the transducing microstructure (3); a protective membrane (17; 117; 217; 317) made of a porous polysilicon layer and permeable to a gaseous substance, the protective membrane (17; 117; 217; 317) being arranged so as to span the passage (15; 115; 315).

[0059] The protective film (17; 117; 217; 317) can be positioned along the channel at a midpoint location between the second face (5b; 105b; 205b; 305b) and the first face (5a; 105a; 205a; 305a).

[0060] The protective film (17; 117; 217; 317) can have pores with an equivalent diameter comprised between 5 nm and 50 nm.

[0061] The gap (14) can be defined between the first face (5a; 105a; 205a; 305a) of the lid (5; 105; 205; 305) and the substrate (2), and wherein the transducing microstructure (3) is in communication with the channel (15; 115; 315) and the gap (14).

[0062] The device can comprise a porous polysilicon region (18; 118; 218) coated on the side surface (15; 115; 215) of the channel between the protective film (17; 117; 218) and one face between the first face (5a; 105a) and the second face (205a), wherein the protective film (17) can be part of the porous polysilicon region (18; 118; 218).

[0063] The device can comprise a plurality of channels (115; 315) and a plurality of porous polysilicon and gas-gate substance permeable protective films, each protective film (17; 117; 217; 317) being arranged across one of the respective channels (115; 315).

[0064] The electronic system can be summarized as comprising a processing unit (402) and a semiconductor device (1; 100; 200; 300).

[0065] A method for manufacturing a semiconductor device, the method can be summarized as comprising: forming a transducing microstructure (3) in a microstructure semiconductor wafer (2'); forming a stop layer (24; 324) on a bulk layer (4'; 304') of a cap semiconductor wafer (5'; 305'); forming a protective layer (25; 325) made of porous polysilicon and permeable to a gaseous substance on at least a portion of the stop layer (24; 324); forming a passage (15; 115; 315) through the cap semiconductor wafer (5'; 305') extending from a first face (5a; 105a; 205a; 305a) to a second face (5b; 105b; 205b; 305b) thereof, wherein the forming of the passage (15; 115; 315) comprises etching the bulk layer (4'; 304') in an anisotropic manner until the side of the cap semiconductor wafer (5'; 305') opposite the protective layer (25; 325); removing the stop layer within the passage (15; 315); and bonding the cap (5; 105; 205; 305) to the microstructure semiconductor wafer (2') so that the passage (15; 115; 315) will be in communication with the transducing microstructure (3).

[0066] The forming of the passage (15; 115) can comprise forming a recess in the cap semiconductor wafer (5'; 305') and wherein the forming of the protective layer (25; 325) can comprise depositing the protective layer (25; 325) within the recess (23; 345).

[0067] The forming of the recess (23) can comprise opening a trench in the bulk layer (4');

[0068] The forming of the recess (345) can comprise depositing a structure layer (341) on the stop layer (324) and selectively etching the structure layer (341).

[0069] The forming of the protective layer (25; 325) can comprise depositing the protective layer (25; 325) in the recess (23; 345) in direct contact with the stop layer.

[0070] The protective layer (25; 325) can have pores (19) having an equivalent diameter comprised between 5 nm and 50 nm, and wherein the size and density of the pores (19) can be such that the empty / full ratio of the protective layer (25; 325) is comprised between 5% and 30%.

[0071] The forming of the passage (15; 115; 315) can comprise etching the bulk layer (4'; 304') in an anisotropic manner at the location corresponding to the recess (23; 45).

[0072] The method can include forming a plurality of channels (115; 315) through the cover semiconductor wafer (5'; 305') from a first face (5a; 105a; 205a; 305a) to a second face (5b; 105b; 205b; 305b) thereof.

[0073] The method can include forming a plurality of channels (115; 315) through the cover semiconductor wafer (5'; 305') from a first face (5a; 105a; 205a; 305a) to a second face (5b; 105b; 205b; 305b) thereof.

[0074] The various embodiments described above can be combined to provide further embodiments. If desired, aspects of different embodiments can be modified and / or combined to provide additional embodiments.

[0075] These and other changes can be made to the embodiments in light of the above- described detailed description. In general, the terms used in the appended claims should not be construed to limit the claims of the application to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims should not be limited by the disclosure.

Claims

1. A semiconductor device comprising: a substrate; a transducing microstructure in the substrate; a cap coupled to the substrate and having a first face facing the substrate and an external second face; a channel through the cap from the second face to the first face and in fluid communication with the transducing microstructure, the channel including an internal sidewall; a protective film of porous polysilicon spanning the channel and on the internal sidewall of the channel.

2. The device of claim 1, wherein the protective film spanning the channel is at an intermediate position between the second face and the first face.

3. The device of claim 1, wherein protective film has pores having an equivalent diameter included between 5 nm and 50 nm.

4. The device of claim 1, wherein a gap is between the first face of the cap and the substrate and the transducing microstructure and the channel are in fluid communication with the gap.

5. The device of claim 1, wherein the protective film includes a portion on the first face and a portion on the internal sidewall of the channel.

6. The device of claim 1, further comprising a plurality of additional channels and a plurality of additional protective films of porous polysilicon, each additional protective film spanning a respective additional channel of the plurality of additional channels.

7. A device comprising: a substrate; a chamber in the substrate; a membrane aligned with the chamber ； a cap comprising: a first surface facing the membrane; a second surface opposite the first surface; an opening from the first surface to the second surface; a porous silicon layer covering the opening.

8. The device of claim 7, wherein the porous silicon layer includes a first portion on the first surface of the cap and a second portion on an inner wall of the opening.

9. The device of claim 7, wherein the porous silicon layer includes a first portion on the second surface of the cap and a second portion on an inner wall of the opening.

10. The device of claim 7, wherein the cap includes a first extension from the first surface and a second extension from the first surface, the opening being between the first extension and the second extension, the porous silicon layer having an end on the first surface, the end being spaced apart from the inner wall of the opening toward the first extension and the second extension.

11. The device of claim 10, wherein the end is spaced apart from the first extension by a first distance and the end is spaced apart from the second extension by a second distance less than the first distance.

12. A method comprising: forming a transducing microstructure; forming a stop layer on a bulk layer of a cap; forming a protective layer of porous polysilicon on the stop layer, the protective layer being permeable to a gaseous substance; forming a channel through the cap from a first face to a second face, forming the channel including: etching the bulk layer on a side of the cap opposite the protective layer to the stop layer in an anisotropic manner; removing the stop layer within the channel; and coupling the cap to the transducing microstructure using the channel in fluid communication with the microstructure.

13. The method of claim 12, wherein forming the channel comprises: forming a recess in the cap, and wherein forming the protective layer comprises depositing the protective layer within the recess.

14. The method of claim 13, wherein forming the recess comprises: opening a trench in the bulk layer.

15. The method of claim 13, wherein forming the recess comprises: depositing a structure layer on the stop layer and selectively etching the structure layer.

16. The method of claim 13, wherein forming the protective layer comprises: depositing the protective layer in direct contact with the stop layer in the recess.

17. The method of claim 13, wherein the protective layer has pores having an equivalent diameter between 5 nm to 50 nm, and wherein the size and density of the pores are such that the empty / full ratio of the protective layer is comprised between 5% to 30%.

18. The method of claim 13, wherein forming the channel comprises: etching the bulk layer in an anisotropic manner at locations corresponding to the recesses.

19. The method of claim 13, comprising: forming a plurality of additional channels through the cap from the first face to the second face.

20. The method of claim 12, comprising: forming a pedestal extending from the first face of the cap; and forming a coupling coating on the pedestal; wherein coupling the cap to the transducing microstructure comprises engaging the pedestal to the transducing microstructure; wherein the pedestal has a height relative to the first face of the cap to create a gap between the first face and the microstructure.

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