Manufacturing process of microelectromechanical device with improved sealing performance

Abstract

The invention relates to a manufacturing process of a microelectromechanical device with improved sealing performance. A manufacturing process of a micro-electro-mechanical device includes: forming a structural layer and a stop layer on a first wafer; defining a stop pad from the stop layer; forming a first micro-electro-mechanical structure and a second micro-electro-mechanical structure in the structural layer; forming a contact element protruding from the second wafer; sealing, at a first pressure, the first microelectromechanical structure in the first chamber and the second microelectromechanical structure and the stop pad in the second chamber; fluidly coupling the second chamber to an external environment; and sealing the second chamber at the second pressure. Sealing at the first pressure includes bonding the second wafer to the first wafer such that the contact element is disposed on the stop pad. The fluid coupling includes defining a fluid passage at an interface between the contact element and the stop pad, and opening an access hole through the second wafer in communication with the fluid passage.

Description

Technical Field

[0001] The present disclosure relates to a manufacturing process of a microelectromechanical device with improved sealing performance. Background Art

[0002] As is well known, different microelectromechanical devices contained and sealed in the same package are used in many applications. For example, it is very common to integrate a single-axis or multi-axis gyroscope and an accelerometer into the same chip and thus into the same package.

[0003] A common problem is related to the fact that the devices may have very different optimal operating conditions from each other, as in the case of gyroscopes and accelerometers. In fact, in order to reduce the consumption due to air friction damping, it is preferable to operate the gyroscope in an environment with a relatively low pressure, usually between 0.1 millibar (mbar) and 1 mbar. The gyroscope remains in resonance and oscillates continuously, and the low-pressure condition allows the oscillation to be maintained, thus reducing damping and dissipated energy. On the other hand, normally, the accelerometer operates under higher pressure conditions, for example, between 1 mbar and several atmospheres. Other types of devices operating under different conditions (such as resonators or wake-up systems combined with gyroscopes or accelerometers) may also cause similar problems.

[0004] Possible solutions include including different devices in the same cavity or chamber of the package, where there is a pressure level corresponding to a compromise between the preferred operating pressures. The implementation of this type of solution is relatively simple, but it may be unsatisfactory and affect performance.

[0005] According to a different solution, the microelectromechanical devices are included in corresponding sealed and non-connected chambers. In practice, the devices (such as gyroscopes and accelerometers) are fabricated in a first wafer, while in a second wafer, a lid is provided and cavities are formed at positions corresponding to the respective devices. In the cavities intended for the devices operating at a lower pressure, an absorbent material or a getter layer is also deposited. When the second wafer is bonded to the first wafer, for example, by frit bonding or other wafer bonding techniques, or at a later time with a dedicated step, the getter is thermally activated to absorb the non-inert gases present in the chamber, thereby reducing the pressure. In this way, the chambers sealed at different pressures and the corresponding devices can operate under the preferred pressure conditions.

[0006] However, even this last solution is not without limitations. First, especially when a particularly high pressure is desired in one of the chambers, the amount of gaseous nitrogen available may saturate the getter, and in such cases, the pressure target in the chamber may not be achievable. On the other hand, to prevent saturation by including a sufficient amount of getter, the size of the chamber (bottom area and / or height) may be larger than would be sufficient for individual microelectromechanical devices.

[0007] In addition, during manufacturing, the getter may be prematurely activated during the wafer bonding step before the chamber is fully sealed. In such cases, the getter can also absorb gas from the higher pressure chamber (crosstalk), resulting in a twofold drawback. On the one hand, in fact, the pressure in the non-getter chamber is reduced, and in any case, the final pressure value cannot be accurately predicted. On the other hand, the getter may become saturated more easily, so that even in the low pressure chamber, the atmosphere cannot reach the desired level. Summary of the Invention

[0008] The present disclosure relates to overcoming or at least partially alleviating the drawbacks and limitations of the prior art.

[0009] The present disclosure relates to at least one embodiment of a manufacturing process for microelectromechanical devices.

[0010] For example, at least one embodiment of a process for manufacturing a microelectromechanical device according to the present disclosure is generally summarized as including: forming a dielectric layer, a structural layer, and a stop layer on a first semiconductor wafer including a semiconductor material; defining a stop pad from the stop layer; forming a first microelectromechanical structure and a second microelectromechanical structure in the structural layer; forming a contact element protruding on the face of a second semiconductor wafer, the contact element being selectively etchable relative to the stop layer; sealing the first microelectromechanical structure in a first chamber and the second microelectromechanical structure and the stop pad in a second chamber at a first pressure; fluidly coupling the second chamber to the external environment through the second semiconductor wafer; and sealing the second chamber at a second pressure different from the first pressure, wherein sealing the first microelectromechanical structure and the second microelectromechanical structure includes bonding the second semiconductor wafer to the first semiconductor wafer such that the contact element is disposed on the stop pad, and wherein fluid coupling includes defining a fluid passage at the interface between the contact element and the stop pad, and opening an access hole leading to the second chamber, the access hole passing through the second semiconductor wafer up to the stop pad and communicating with the fluid passage. Brief Description of the Drawings

[0011] To better understand the present disclosure, preferred embodiments are now provided by way of non-limiting example with reference to the accompanying drawings, wherein:

[0012] Figure 1 、 Figure 3a 、 Figure 4, Figure 5a , Figure 6a , Figure 7a , Figure 8 Schematically shows, in the same cross-section, consecutive processing steps of the manufacturing process of a MEMS device according to an embodiment of the present disclosure;

[0013] Figure 2a and Figure 3b Schematically shows, in a top view, consecutive processing steps of the manufacturing process of a MEMS device according to an embodiment of the present disclosure;

[0014] Figure 2b , Figure 3c , Figure 5c , Figure 6c , Figure 7c Schematically shows, in the same cross-section, a magnified portion of the MEMS device in consecutive processing steps of the manufacturing process according to an embodiment of the present disclosure;

[0015] Figure 2c , Figure 3d , Figure 5d , Figure 6d , Figure 7d Schematically shows, in the same cross-section, different magnified portions of the MEMS device in consecutive processing steps of the manufacturing process according to an embodiment of the present disclosure;

[0016] Figure 5b , Figure 6b , Figure 7b Schematically shows, in a top view, a magnified portion of the MEMS device in consecutive processing steps of the manufacturing process according to an embodiment of the present disclosure;

[0017] Figure 9a , Figure 9c , Figure 9e Schematically shows, in the same cross-section, a magnified portion of the MEMS device in consecutive processing steps of the manufacturing process according to different embodiments of the present disclosure;

[0018] Figure 9b , Figure 9d , Figure 9f Schematically shows, in the same cross-section, different magnified portions of the MEMS device in consecutive processing steps of the manufacturing process according to different embodiments of the present disclosure;

[0019] Figure 10a Schematically shows, in a top view, the MEMS device in the processing steps of the manufacturing process according to another embodiment of the present disclosure;

[0020] Figure 10b and Figure 10b1 Schematically shows, in top views relative to each other, Figure 10a the magnified portion of

[0021] Figure 10c 、 Figure 10e 、 Figure 10g Schematically shows, in the same cross-section, the enlarged portion of the MEMS device in successive processing steps of a manufacturing process according to another embodiment of the present disclosure; and

[0022] Figure 10d 、 Figure 10f 、 Figure 10h Schematically shows, in the same cross-section, different enlarged portions of the MEMS device in successive processing steps of a manufacturing process according to another embodiment of the present disclosure. Detailed Description

[0023] In Figure 1 a semiconductor wafer shown in cross-section, or simply "wafer" 1, includes a substrate 2, such as single-crystalline silicon. A first region 1a of the wafer 1 is intended to accommodate a first microelectromechanical sensor, such as an accelerometer, operating at a first pressure P1, and a second region 1b of the wafer 1 is intended to accommodate a second microelectromechanical sensor, such as a gyroscope, operating at a second pressure P2 lower than the first pressure. However, it should be understood that other microelectromechanical devices requiring different operating pressures can be integrated into the wafer 1, such as, but not limited to, resonators, wake-up systems, geophones, bolometers.

[0024] Considering a reference system of orthogonal axes X, Y, Z, the wafer 1 has a substantially planar shape parallel to the XY plane and includes semiconductor material layers stacked in the Z-axis direction as described below.

[0025] Initially, a dielectric layer 3 of silicon oxide is deposited on the substrate 2. Conductive traces 4, such as suitably doped polysilicon, are formed in the dielectric layer 3: the conductive traces 4 can include, for example, fixed electrodes of the respective sensors and / or buried electrical connections. Subsequently, a structural layer 5, such as polysilicon, is formed on the dielectric layer 3: for example, the structural layer 5 is grown using an epitaxial reactor.

[0026] Referring to Figures 2a to 2c , the subsequent processing of the structural layer 5 is carried out so as to generate, for example, grooves 6 by anisotropic etching. The grooves 6 are organized into multiple groups, and each group forms a pattern in the structural layer 5. In a non-limiting embodiment, there is only one group of grooves 6 arranged radially (see Figure 2a ). In fact, the grooves 6 are material removal portions in the structural layer 5, the depth of which along the Z axis is, for example, between 0.1 μm and 0.5 μm. The grooves 6 are formed in the structural layer 5 in a part of the second region 1b of the wafer 1, for reasons described below, for example, in the structural layer in the lateral part of the second region 1b.

[0027] Subsequently, a stop layer 7 having a thickness, for example, between 0.2 μm and 1 μm (preferably 0.7 μm) is deposited on the structural layer 5. The stop layer 7 generally contains a material with respect to which the structural layer 5 (more particularly, silicon) is selectively etchable. In a non-limiting embodiment, the stop layer 7 contains aluminum; alternatively, the stop layer 7 is a titanium-tungsten (TiW) compound. Subsequently, the stop layer 7 is patterned (e.g., lithographically) to form a frame portion 7a, a separation portion 7b, and a stop pad 7c. Specifically, referring to Figure 3a and Figure 3b , the frame portion 7a surrounds the first region 1a and the second region 1b of the wafer 1, and the separation portion 7b separates the first region 1a from the second region 1b. The frame portion 7a and the separation portion 7b are, for example, structurally continuous.

[0028] The stop pad 7c of the stop layer 7 is formed at least in part on a corresponding set of grooves 6. Specifically, referring to Figure 3c ( Figure 3a an enlarged view of the same cross-section of Figure 3d ), the stop pad 7c fills the grooves 6, which is obtained by transferring the previously defined pattern of the grooves 6. Thus, the stop layer 7 remains conformal to the profile of the structural layer 5, particularly replicating its pattern in the stop pad 7c. Thus, the stop pad 7c defines the channels 8 as a first approximation corresponding to the respective grooves 6 of the structural layer 5; in addition, the channels 8 cover a distance along the Z-axis over the respective grooves 6 that is a first approximation equal to the thickness of the stop layer 7.

[0029] Referring to Figure 4 , subsequently, the structural layer 5 is processed, for example, by one or more anisotropic etching processes to define a first microelectromechanical structure 9a of the first sensor and a second microelectromechanical structure 9b of the second sensor in the first region 1a and the second region 1b of the wafer 1, respectively. For example, structures suspended and movable with respect to the substrate 2 and corresponding flexures can be defined to expose the structural layer 5 and remove portions of the underlying dielectric layer 3.

[0030] A cover wafer 10 of semiconductor material (e.g., single-crystalline silicon or polycrystalline silicon) is separately fabricated and processed on the inner face 10' facing the semiconductor wafer 1 in the final device. Specifically, contact elements 11, a first cavity 10a, and a second cavity 10b are formed on the inner face 10'. The cover wafer 10 is shaped to include the first sensor and the second sensor in the respective chambers when bonded to the semiconductor wafer 1. Specifically, the contact elements 11 are protrusions of the cover wafer 10 and are configured to allow bonding between the cover wafer 10 and the semiconductor wafer 1, as described below; the first cavity 10a and the second cavity 10b are recesses of the cover wafer 10 and are formed at positions corresponding to the respective first region 1a and second region 1b of the wafer 1 to allow the first sensor and the second sensor to operate according to the design specifications.

[0031] Refer to Figure 5a , the cover wafer 10 is bonded to the semiconductor wafer 1 (a step of "wafer-to-wafer bonding"); this bonding refers to the composite wafer 20, and it should be understood that this is performed along the direction of the Z axis (the composite wafer 20 is shown with the same cross-section as Figure 1 , Figure 3a and Figure 4 the same). In one embodiment, the cover wafer 10 is bonded to the wafer 1 by a bonding layer 12 (such as a germanium-aluminum (AlGe) compound) and using, for example, a thermal bonding process. Alternative compounds for the bonding layer 12 can be: gold-germanium (Au-Ge); gold-indium (Au-In); gold-silicon (Au-Si); gold-tin (Au-Sn); copper-tin (Cu-Sn).

[0032] Specifically, the contact elements 11 are formed at positions on the cover wafer 10 corresponding to the previously defined portions of the stop layer 7 of the wafer 1. With particular reference to: a first contact element 11a, which is defined starting from the cover wafer 10 to be bonded to the frame portion 7a; and a second contact element 11b, which is defined to be bonded to the separation portion 7b. The first contact element 11a and the second contact element 11b extend along the entire dimensions of the frame portion 7a and the separation portion 7b parallel to the XY plane (for example, the first contact element 11a extends in a plane parallel to the XY plane forming the frame). In addition, refer to a third contact element 11c, which is defined starting from the cover wafer 10 to contact the stop pad 7c.

[0033] The bonding layer 12 is applied to the cover wafer 10 and is defined to externally coat the first contact element 11a and the second contact element 11b. During the bonding process used, the bonding layer 12 allows bonding between the material of the cover wafer 10 and the material of the stop layer 7. In a non-limiting embodiment, the cross-section of the contact element 11 (a plane parallel to the XZ plane) has a substantially trapezoidal shape and extends along the X axis, and its minimum dimension is less than or equal to the corresponding dimension of the defined portion of the stop layer 7. Specifically, when observed in a plane parallel to the XY plane, the third contact element 11c has, for example, a substantially rectangular cross-section (i.e., in three dimensions, as a first approximation, it is frustoconical).

[0034] Refer again to Figure 5a, the composite wafer 20 includes a first chamber 15a and a second chamber 15b disposed at positions substantially corresponding to the first region 1a and the second region 1b of the wafer 1, respectively. The tops of the first chamber 15a and the second chamber 15b are defined by the cover wafer 10 and the bottoms are defined by the wafer 1. They are surrounded by the first contact element 11a and separated from each other by the second contact element 11b and the separation portion 7b. Accordingly, the first chamber 15a and the second chamber 15b include a first microelectromechanical sensor and a second microelectromechanical sensor, respectively.

[0035] The process of bonding the cover wafer 10 to the wafer 1 is performed in an atmosphere at a first pressure P1, and the first chamber 15a is hermetically sealed relative to the environment outside the composite wafer 20. Accordingly, the first chamber 15a is sealed at the first pressure P1 and maintains the first pressure P1; thus, the first sensor of the final device operates at the first pressure P1. The first pressure P1 is, for example, between 1 mbar and several atmospheres (atm). Bonding the cover wafer 10 to the wafer 1 also effectively hermetically seals the second chamber 15b relative to the external environment: however, this second chamber undergoes other processes as described below. The second contact element 11b of the cover wafer 10 ensures a hermetic separation between the first chamber 15a and the second chamber 15b, such that subsequent processes performed on the second chamber 15b do not affect the pressure conditions formed in the first chamber 15a (i.e., crosstalk between the chambers is eliminated).

[0036] In Figures 5b to 5d , what happens during the process of bonding the cover wafer 10 to the positions corresponding to the stop pad 7c and the third contact element 11c of the wafer 1 can be observed (in Figure 5b , the stop pad 7c and the channel 8 are shown enlarged, and some parts have been removed for clarity of understanding). The third contact element 11c directly contacts the stop pad 7c in the absence of the channel 8; in addition, the third contact element 11c at least partially covers the channel 8. More specifically, the third contact element 11c is defined starting from the cover wafer 10 and extends with a smaller dimension parallel to the XY plane with respect to the two-dimensional pattern defined by the channel 8. In this way, the ends of the channel 8 protrude laterally with respect to the third contact element 11c and remain at least partially in communication with the second chamber 15b.

[0037] As the exchange region 17, refer to the overlapping region of the third contact element 11c on the stop pad 7c. The exchange region 17 is a volume including the interface portion of the stop pad 7c and the interface portion of the third contact element 11c (see specifically Figure 5c and Figure 5d ). Accordingly, the exchange region 17 includes the channel 8 of the stop pad 7c covered by the third contact element 11c.

[0038] Subsequently, there is a known intermediate grinding and finishing process of the outer surfaces of the composite wafer 20 and, in particular, of the cover wafer 10.

[0039] Now referring Figures 6a to 6d , in a position corresponding to the third contact element 11c and thus to the stop pad 7c, an access hole (also called chimney) 13 passing through the entire cover wafer 10 is provided. After the access hole 13 is provided, the third contact element 11c remains internally hollow: parallel to the XY plane, the access hole 13 has a size smaller than that of the third contact element 11c. Thus, the access hole 13 communicates with the second chamber 15b through the channel 8.

[0040] For example, the access hole 13 can be provided by selectively etching the cover wafer 10. Due to the presence of the stop pad 7c, the etching stops at the interface between the third contact element 11c and the stop pad 7c without affecting the structural layer 5: the etching selectivity of the material of the structural layer 5 and the cover wafer 10 (silicon) with respect to the material of the stop layer 7 (aluminum) in fact allows accurate control of the definition of the access hole 13. In a non-limiting embodiment, the access hole 13 has a circular cross-section (see Figure 6b ), and has a diameter, for example, between 20 μm and 30 μm.

[0041] The access hole 13 is a through-hole of the cover wafer 10, and the second chamber 15b communicates with the environment outside the composite wafer 20 through the exchange area 17. Specifically, the channel 8 of the stop pad 7c forms a fluid passage that allows fluid exchange between the inside of the second chamber 15b, which is initially at the first pressure P1, and the external environment after the bonding process between the cover wafer 10 and the wafer 1. For example, the access hole 13 can be used to remove the substances degassed from the structural layer 5 during the bonding process from the second chamber 15b (which is intended to include the second sensor, which requires, for example, more stringent and controlled operating conditions, such as a gyroscope).

[0042] Then, the Figures 6a to 6d composite wafer 20 is placed in a controlled atmosphere at the second pressure P2. Through the access hole 13 and through the exchange area 17, the second chamber 15b reaches the second pressure P2 preset for the operation of the corresponding second sensor. The second pressure P2 is, for example, between 0.1 mbar and 1 mbar.

[0043] Subsequently, referring Figures 7a to 7d , the composite wafer 20 is completely coated with the sealing layer 14, while the access hole 13 is closed with respect to the external environment. Specifically, the sealing layer 14 penetrates the access hole 13 at least up to the stop pad 7c, thereby filling the part of the channel 8 exposed by the access hole 13 in the exchange area 17 (see Figure 7c and Figure 7d(details). The deposition of the sealing layer 14 is performed in an atmosphere at a second pressure P2, and the second chamber 15b is hermetically sealed with respect to the environment outside the composite wafer 20. Thus, the second chamber 15b is sealed at the second pressure P2 and maintained at the second pressure P2; thus, the second sensor of the final device operates at the second pressure P2.

[0044] The sealing layer 14 is selected, for example, from among the following substances and / or compounds of substances: TEOS (tetraethyl orthosilicate), SiN (silicon nitride), SiON (silicon oxynitride), TEOS+SiN, TEOS+SiON, TEOS+SiN+AlCu (aluminum-copper alloy). This selection can depend, for example, on the required degree of sealing and mechanical integrity. The sealing process through the sealing layer 14 can be performed at the second pressure P2 using, for example, PECVD (plasma-enhanced chemical vapor deposition) technology or PVD (physical vapor deposition) technology.

[0045] Finally, referring to Figure 8 , the composite wafer 20 undergoes a final grinding process, a wet cleaning and drying process (for example, by vacuum perfusion-vacuum drying), and the final grinding process causes, for example, the cover wafer 10 to become thinner. Then, external contacts and pads for driving and extracting signals are defined; more generally, the operations necessary to define the final device including the first sensor and the second sensor (and having Figure 8 the structure shown in

[0046] The manufacturing process of the present disclosure allows the operating conditions of the chambers accommodating different microelectromechanical sensors integrated into the final device to be independently adjusted. In particular, by means of the proposed process, the optimal pressure and / or operating gas composition can be selected for each sensor in a flexible and accurate manner in successive steps, thus eliminating problems related to crosstalk between different chambers. In this way, the devices manufactured by means of this process have performance characteristics with a lower tendency to drift over time and are ultimately more reliable.

[0047] Figures 9a to 9f illustrates details of different embodiments of the subject matter of the manufacturing process of the present disclosure. The elements corresponding to the Figures 1 to 8 elements of Figures 9a to 9f are indicated by the same reference numerals, and the differences with respect to the previously described embodiments are shown.

[0048] Referring to Figure 9a and Figure 9b (which shows the differences with respect to Figure 3c and Figure 3dDetail of the cross section of wafer 1 similar to that of wafer 1), stop layer 7 is deposited on structure layer 5 (without first defining groove), and is patterned to define frame portion 7a, separation portion 7b (not shown here) and stop pad 57c. In this step, channel 58 is opened in the inner portion of stop pad 57c. In particular, stop pad 57c is similar in shape and positioning in wafer 1 to stop pad 7c (see Figure 3b ), and the channel 58 of the stop pad 57c is organized with Figure 2a The pattern of the grooves 6 of the structured layer 5 of the embodiment is similar to the pattern.

[0049] The channel 58 of the stop pad 57c can be formed simultaneously with the patterning of the stop layer 7, or formed by a dedicated anisotropic etch and completely penetrates the stop pad 57c to the structural layer 5. In other words, the channel 58 leaves exposed parts of the structural layer 5 according to a predetermined pattern. The exchange region 17 includes the channel 58 of the stop pad 57c covered by the third contact element 11c.

[0050] According to what has been described previously, the lid wafer 10 is bonded to the wafer 1, and the first chamber 15a is sealed at the first pressure P1. Figure 9c and Figure 9d ) in a position corresponding to the stop pad 57c, thereby leaving an exposed portion of the channel 58 (i.e., a corresponding portion of the structural layer 5) in the exchange region 17, similar to Figure 6b Therefore, the channel 58 forms a fluid passage like the channel 8 of the stop pad 7 c , which allows the second chamber 15 b to communicate with the environment outside the composite wafer 20 through the exchange area 17 and the inlet and outlet holes 13 .

[0051] Then, the composite wafer 20 is placed in an atmosphere at a second pressure P2 , and the sealing layer 14 is deposited on the cap wafer 10 . Figure 9e and Figure 9f (It is relative to Figure 7c and Figure 7d Detail of the cross section of the wafer 1 similar to those of FIG. 1 ) shows in detail the sealing layer 14 at the stop pad 57c. In this embodiment, the sealing layer 14 contacts the stop pad 57c and the structural layer 5, thereby filling the portion of the channel 58 in the exchange area 17 exposed by the inlet and outlet holes 13. Therefore, the second chamber 15b is hermetically closed relative to the environment outside the composite wafer 20 at the second pressure P2.

[0052] Figures 10a to 10h Detail of another embodiment of the manufacturing process subject matter of the present disclosure is illustrated. Figures 1 to 8 The components corresponding to Figures 10a to 10h Elements are indicated with the same reference numerals and the differences with respect to previously described embodiments are shown.

[0053] Reference Figure 10a and Figure 10b , the structural layer 5 of this embodiment has no grooves. In addition, the stop layer 7 includes a stop pad 107c, which is similar to the stop pad 7c in shape and in its positioning in the wafer 1 (see Figure 3b ), and also has no grooves. In this embodiment, the cover wafer 10 includes a first contact element 11a, a second contact element 11b, and a third contact element 111c, which is similar to the third contact element 11c in shape and in its positioning in the cover wafer 10.

[0054] Before bonding the cover wafer 10 to the semiconductor wafer 1, a surface channel 108 is formed at one end of the third contact element 111c (also see Figure 10c and Figure 10d for two different cross-sections), and this surface channel extends from one side to the other along the contact surface 111d of the third contact element 111c parallel to the XY plane (see Figure 10b1 ), and is organized, for example, into a pattern similar to the channels of the previous embodiment.

[0055] According to what has been previously described, the cover wafer 10 is bonded to the wafer 1 while sealing the first chamber 15a under the first pressure P1. The third contact element 111c is placed on the stop pad 107c, which is wider than the contact surface 111d and defines one side (parallel to the XY plane) of the channel 108. The exchange region 17 includes the channel 108 of the third contact element 111c.

[0056] Then, access holes 13 are provided in the cover wafer 10 ( Figure 10e and Figure 10f ) at positions corresponding to the stop pad 107c, so that a part of the stop pad 107c is exposed in the exchange region 17. Thus, the remaining part of the channel 108 forms a fluid passage that connects the second chamber 15b to the environment outside the composite wafer 20 through the exchange region 17 and the access holes 13.

[0057] Then, the composite wafer 20 is placed in an atmosphere at the second pressure P2, and a sealing layer 14 is deposited on the cover wafer 10. In Figure 10g and Figure 10h , the sealing layer 14 is shown in detail at the stop pad 107c. In this embodiment, the sealing layer 14 contacts, for example, up to the thickness of the third contact element 111c with the exposed part of the stop pad 107c so as to cover it; the sealing layer 14 may also fill at least a part of the remaining part of the channel 108 of the third contact element 111c. Thus, the second chamber 15b is hermetically sealed relative to the environment outside the composite wafer 20 under the second pressure P2.

[0058] Finally, it is clear that modifications and variations can be made to what has been described and illustrated herein without departing from the scope of the disclosure as defined in the appended claims.

[0059] For example, the pattern of channels obtained in a semiconductor wafer or a lid wafer can have a shape different from the previously illustrated shape while still ensuring a fluid connection of one of the device chambers to the outside. Additionally, although a unique set of channels has been presented in the foregoing description, it should be understood that the semiconductor wafer or the lid wafer can be processed to include multiple sets of channels, which can also differ from each other in pattern depending on the desired sealing performance and / or depending on the number of chambers of the device. In an embodiment not shown, the fluid passageways can be formed by a structure including hybrid characteristics of the previously described solutions: for example, the fluid passageways can include channels defined both on the semiconductor wafer (e.g., on the stop pads) and on the lid wafer (on the third contact elements).

[0060] Regarding the contact elements of the lid wafer, it should be understood that their cross-sections can have a shape different from the presented shape. For example, the third contact element can have a three-dimensional cylindrical shape.

[0061] During the process of bonding the lid wafer to the semiconductor wafer, a wafer-wafer bonding technique different from the one shown can be used. In a variant not shown, for example, the lid wafer only includes the third contact element, and the bonding to the semiconductor wafer (and the separation between the chambers) is performed by frit bonding (a bonding technique using a glassy intermediate layer).

[0062] The first pressure and the second pressure respectively enclosing the first chamber and the second chamber of the device can have a relationship different from the one described. In particular, the first pressure can be lower than the second pressure.

[0063] Finally, in addition to inertial sensors, the process according to the present disclosure can be extended to the manufacture of devices (such as, for example, bolometers and geophones) that require a high vacuum level (pressure in the order of microbars) during the packaging step.

[0064] At least one embodiment of a process for manufacturing microelectromechanical devices according to the present disclosure is generally described as including: forming a dielectric layer (3), a structural layer (5), and a stop layer (7) on a first semiconductor wafer (1) including a substrate (2) of semiconductor material; defining a stop pad (7c; 57c; 107c) from the stop layer (7); forming a first microelectromechanical structure (9a) and a second microelectromechanical structure (9b) in the structural layer (5); forming contact elements (11c; 111c) protruding on a face (10′) of a second semiconductor wafer (10), the contact elements being selectively etchable relative to the stop layer (7); sealing the first microelectromechanical structure (9a) in a first chamber (15a) and the second microelectromechanical structure (9b) in a second chamber (15b) and the stop pad (7c; 57c; 107c) under a first pressure (P1); fluidly coupling the second chamber (15b) to the external environment through the second semiconductor wafer (10); and sealing the second chamber (15b) under a second pressure (P2) different from the first pressure (P1), wherein sealing the first microelectromechanical structure (9a) and the second microelectromechanical structure (9b) includes bonding the second semiconductor wafer (10) to the first semiconductor wafer (1) such that the contact elements (11c; 111c) are seated on the stop pad (7c; 57c; 107c), and wherein the fluid coupling includes defining a fluid passage (8; 58; 108) at an interface between the contact element (11c; 111c) and the stop pad (7c; 57c; 107c), and opening an access hole (13) leading to the second chamber (15b) that passes through the second semiconductor wafer (10) up to the stop pad (7c; 57c; 107c) and is in communication with the fluid passage (8; 58; 108).

[0065] In at least one embodiment, sealing the first microelectromechanical structure (9a) and the second microelectromechanical structure (9b) includes bonding the second semiconductor wafer (10) to the first semiconductor wafer (1) in an atmosphere under the first pressure (P1).

[0066] In at least one embodiment, defining the fluid passage (8) includes: defining a groove (6) in a position of the structural layer (5) corresponding to the stop pad (7c); and depositing the stop layer (7) conformally on the structural layer (5) with a thickness such that in the stop pad (7c), the fluid passage (8) corresponds in shape and position to the corresponding groove (6) of the structural layer (5).

[0067] In at least one embodiment, defining the fluid passage (58) includes opening a channel (58) in the stop pad (7c) after forming the stop layer (7).

[0068] In at least one embodiment, an end of the fluid passage (8; 58) protrudes laterally relative to the contact element (11c) on the stop pad (7c; 57c).

[0069] In at least one embodiment, defining a fluid passage (108) includes defining a surface channel (108) at one end of a contact element (111c) of a second semiconductor wafer (10).

[0070] In at least one embodiment, opening the access holes (13) includes etching the second semiconductor wafer (10) and stopping the etching on the stop pad (7c; 57c; 107c), and wherein the stop layer (7) includes one or more materials selected from the following materials: aluminum; titanium-tungsten compound.

[0071] In at least one embodiment, the access holes (13) expose a portion of the fluid passage (8; 58; 108).

[0072] In at least one embodiment, sealing the first chamber (15a) and the second chamber (15b) at a first pressure (P1) includes: defining a frame portion (7a) and a separation portion (7b) from a stop layer (7) on the first semiconductor wafer (1), the frame portion defining a first microelectromechanical structure (9a) and a second microelectromechanical structure (9b), the separation portion being between the first microelectromechanical structure (9a) and the second microelectromechanical structure (9b); defining other contact elements (11a, 11b) at positions on the second semiconductor wafer (10) corresponding to the frame portion (7a) and the separation portion (7b) of the stop layer (7); coating the other contact elements (11a, 11b) with a bonding layer (12); and bonding the second semiconductor wafer (10) to the first semiconductor wafer (1) through a thermal bonding process.

[0073] In at least one embodiment, the bonding layer (12) includes one or more materials selected from the following materials: germanium-aluminum compound; gold-germanium compound; gold-indium compound; gold-silicon compound; gold-tin compound; copper-tin compound.

[0074] In at least one embodiment, sealing the second chamber (15b) at a second pressure (P2) may include closing the fluid passage (8; 58; 108).

[0075] In at least one embodiment, sealing the second chamber (15b) at a second pressure (P2) includes forming a sealing layer (14) on the second semiconductor wafer (10) and in the access holes (13).

[0076] In at least one embodiment, the sealing layer (14) closes the fluid passage (8; 58; 108) inside the access holes (13).

[0077] In at least one embodiment, the sealing layer (14) may include one or more materials selected from the following materials: tetraethyl orthosilicate; silicon nitride; silicon oxynitride; tetraethyl orthosilicate and silicon nitride compounds; tetraethyl orthosilicate and silicon oxynitride compounds; tetraethyl orthosilicate, silicon nitride and aluminum-copper alloy compounds.

[0078] At least one embodiment of a microelectromechanical device is generally described as including: a substrate (2) of semiconductor material; a dielectric layer (3) on the substrate (2); a structural layer (5) of semiconductor material on the dielectric layer (3); a stop layer (7) on the structural layer (5); in the structural layer (5), a first microelectromechanical structure (9a) sealed in a first chamber (15a) at a first pressure (P1) and a second microelectromechanical structure (9b) sealed in a second chamber (15b) at a second pressure (P2); a stop pad (7c; 57c; 107c) defined from the stop layer (7) in the second chamber (15b); a lid (10) that can be selectively etched relative to the stop pad (7c; 57c; 107c) and that defines the first chamber (15a) and the second chamber (15b), wherein the lid (10) includes a protruding contact element (11c; 111c) disposed on the stop pad (7c; 57c; 107c); an access hole (13) that extends through the lid (10) to the stop pad (7c; 57c; 107c); a fluid passage (8; 58; 108) between the access hole (13) and the second chamber (15b) at the interface between the contact element (11c; 111c) and the stop pad (7c; 57c; 107c); and a sealing layer (14) that closes the fluid passage (8; 58; 108) and fluidly isolates the second chamber (15b) from the access hole (13).

[0079] In at least one embodiment, the fluid passage includes a channel (8; 58) in the stop pad (7c; 57c).

[0080] In at least one embodiment, the fluid passage includes a surface channel (108) at an end of the contact element (111c) disposed on the stop pad (107c).

[0081] The various embodiments described above may be combined to provide other embodiments. If necessary, aspects of the embodiments may be modified to incorporate the concepts of various patents, applications, and publications to provide other embodiments.

[0082] These and other changes may be made to the embodiments in light of the foregoing description. Generally, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and claims, but should be construed to include all possible embodiments within the entire scope of equivalents of the rights conferred by such claims. Accordingly, the claims are not limited by the disclosure.

Claims

1. A method for manufacturing a micro-electromechanical device, comprising: On a first semiconductor wafer including a substrate of semiconductor material, forming a dielectric layer, a structural layer, and a stop layer on the structural layer; defining a stop pad from said stop layer; forming a first micro-electromechanical structure and a second micro-electromechanical structure in the structural layer; forming a contact element protruding on the surface of the second semiconductor wafer, wherein the contact element can be selectively etched relative to the stop layer; sealing the first microelectromechanical structure in the first chamber and the second microelectromechanical structure and the stop pad in the second chamber at a first pressure; fluidly coupling the second chamber to an external environment through the second semiconductor wafer; and sealing the second chamber at a second pressure different from the first pressure, wherein sealing the first microelectromechanical structure and the second microelectromechanical structure comprises bonding the second semiconductor wafer to the first semiconductor wafer such that the contact element is disposed on the stop pad, and The fluid coupling includes defining a fluid passage at the interface between the contact element and the stop pad, and opening an inlet and outlet hole leading to the second chamber, wherein the inlet and outlet hole passes through the second semiconductor wafer to the stop pad and communicates with the fluid passage.

2. The method of claim 1 , wherein sealing the first micro-electromechanical structure and the second micro-electromechanical structure comprises: The second semiconductor wafer is bonded to the first semiconductor wafer in an atmosphere at the first pressure.

3. The method of claim 1 , wherein defining the fluid pathway comprises: defining a groove in the structural layer at a location corresponding to the stop pad; as well as The stop layer is deposited conformally on the structural layer, the stop layer having a thickness such that in the stop pad, the fluid passage corresponds in shape and position to the corresponding groove of the structural layer. 4 . The method of claim 1 , wherein defining the fluid passage comprises opening a channel in the stop pad after forming the stop layer.

5. The method of claim 1, wherein an end of the fluid passage protrudes laterally above the stop pad relative to the contact element. 6 . The method of claim 1 , wherein defining the fluid passage comprises defining a surface channel at an end of the contact element of the second semiconductor wafer.

7. The method of claim 1, wherein opening the access hole comprises etching the second semiconductor wafer and stopping the etching on the stop pad, and The stop layer includes one or more materials selected from the following materials: aluminum; titanium-tungsten compound.

8. The method of claim 1, wherein the access hole exposes a portion of the fluid passageway.

9. The method of claim 1 , wherein sealing the first chamber and the second chamber at the first pressure comprises: defining a frame portion and a separation portion from the stop layer on the first semiconductor wafer, the frame portion defining the first micro-electromechanical structure and the second micro-electromechanical structure, the separation portion being between the first micro-electromechanical structure and the second micro-electromechanical structure; defining other contact elements in locations on the second semiconductor wafer corresponding to the frame portion and the separation portion of the stop layer; coating the further contact element with a bonding layer; as well as The second semiconductor wafer is bonded to the first semiconductor wafer through a thermal bonding process.

10. The method of claim 9, wherein the bonding layer comprises one or more materials selected from the following materials: germanium-aluminum compound; gold-germanium compound; gold-indium compound; gold-silicon compound; gold-tin compound; copper-tin compound.

11. The method of claim 1 , wherein sealing the second chamber at the second pressure comprises closing the fluid passageway. 12 . The method of claim 1 , wherein sealing the second chamber at the second pressure comprises forming a sealing layer on the second semiconductor wafer and in the access hole.

13. The method of claim 12, wherein the sealing layer closes the fluid passage inside the access hole.

14. The method according to claim 12, wherein the sealing layer comprises one or more materials selected from the following materials: tetraethyl orthosilicate; silicon nitride; silicon oxynitride; tetraethyl orthosilicate and silicon nitride compound; tetraethyl orthosilicate and silicon oxynitride compound; tetraethyl orthosilicate, silicon nitride and aluminum-copper alloy compound.

15. A micro-electromechanical device, comprising: Substrates of semiconductor materials; a dielectric layer on the substrate; a structured layer of semiconductor material on the dielectric layer; a stop layer on the structural layer; In the structural layer, a first micro-electromechanical structure sealed in a first chamber at a first pressure and a second micro-electromechanical structure sealed in a second chamber at a second pressure; a stop pad defined by the stop layer in the second chamber; a cover capable of being selectively etched relative to the stop pad and defining the first chamber and the second chamber, wherein the cover includes a protruding contact element disposed on the stop pad; an access hole extending through the cover to the stop pad; a fluid passage between the access hole and the second chamber at an interface between the contact element and the stop pad; as well as A sealing layer closes the fluid passage and fluidically isolates the second chamber from the inlet and outlet holes.

16. The device of claim 15, wherein the fluid passage comprises a channel in the stop pad.

17. The device of claim 15, wherein the fluid passage comprises a surface channel at an end of the contact element disposed on the stop pad.

18. A device comprising: substrate; a dielectric layer on the substrate; a structural layer on the dielectric layer; a stop layer on the structural layer; a first microelectromechanical structure sealed in the first chamber at a first pressure and a second microelectromechanical structure sealed in the second chamber at a second pressure; a stop pad defined by the stop layer in the second chamber, the stop pad including a channel extending into the stop pad; a cover, the cover including an access hole, the access hole overlapping the stop pad; as well as A sealing layer is located within the access hole and adjacent to the stop pad, and the sealing layer seals the channel defined by the stop pad. The device of claim 18 , wherein the sealing layer partially fills the access hole.

20. The device of claim 18, wherein the sealing layer covers a surface of the cover facing away from the substrate and covers one or more side walls of the cover defining and delimiting the access hole.

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