阅读说明：本技术 用于制造mems压力传感器的方法和相应的mems压力传感器 (Method for producing a MEMS pressure sensor and corresponding MEMS pressure sensor ) 是由 L·巴尔多 S·泽尔比尼 E·杜奇 于 2016-09-29 设计创作，主要内容包括：本公开的实施例涉及一种用于制造MEMS压力传感器的方法和相应的MEMS压力传感器。一种用于制造具有微机械结构的MEMS压力传感器的方法设想：提供具有半导体材料的和顶表面的衬底的晶片；形成掩埋腔,该掩埋腔被完全包含在衬底内并且由悬挂在掩埋腔上方的薄膜与顶表面分隔开；形成用于以必须要确定其的值的一压力设定的薄膜与外部环境的流体连通的流体连通通路；形成被悬挂在薄膜上方的由导电材料制成的由空白空间与薄膜分隔开的板区；以及形成用于薄膜和板区的电连接的电接触元件,该电接触元件被设计为形成感测电容器(C)的板,感测电容器的电容值指示要被检测的压力的值。此外,描述了具有微机械结构的对应的MEMS压力传感器。(Embodiments of the present disclosure relate to a method for manufacturing a MEMS pressure sensor and a corresponding MEMS pressure sensor. A method for producing a MEMS pressure sensor having a micromechanical structure envisages: providing a wafer having a substrate of semiconductor material and a top surface; forming a buried cavity that is completely contained within the substrate and separated from the top surface by a thin film suspended over the buried cavity; forming a fluid communication passage for fluid communication of the membrane with the external environment at a pressure setting for which the value has to be determined; forming a plate region made of a conductive material suspended over the thin film and separated from the thin film by a blank space; and an electrical contact element forming an electrical connection for the membrane and the plate area, the electrical contact element being designed to form a plate of a sensing capacitor (C), a capacitance value of the sensing capacitor being indicative of a value of the pressure to be detected. Furthermore, a corresponding MEMS pressure sensor with a micromechanical structure is described.)

1. A method for fabricating a MEMS pressure sensor, the method comprising:

forming a cavity in a substrate of silicon material;

forming a membrane suspended at the cavity;

forming a conductive layer suspended over the membrane, the conductive layer comprising a plate separated from the membrane by an empty space, the plate being made of polysilicon, wherein forming the plate comprises:

a sacrificial layer at a top surface of the substrate;

growing the conductive layer on the sacrificial layer;

forming a plurality of vias in the conductive layer; and

partially removing the sacrificial layer through the plurality of vias and releasing a portion of the conductive layer relative to the substrate, wherein partially removing the sacrificial layer forms the plate and the empty space above the thin film;

forming a via channel providing fluid communication between the membrane and an external environment; and

forming electrical contact elements electrically coupled to the membrane and the plate, respectively, wherein the membrane and the plate form a sensing capacitor, wherein forming the electrical contact elements comprises:

forming a first contact trench through the conductive layer until reaching the sacrificial layer;

forming a second contact trench through the conductive layer and the sacrificial layer until reaching the top surface of the substrate;

forming a conductive region over the conductive layer and within the first and second contact trenches; and

the conductive area is defined by etching and a first electrical contact element of the membrane for electrical connection from the outside and a second electrical contact element of the plate for electrical connection from the outside are formed.

2. The method of claim 1, wherein forming the cavity comprises:

forming a trench within the substrate at a top surface, the trench defined by a pillar of the substrate;

epitaxially growing a closing layer of silicon material at the pillar, the closing layer closing the trench at a top portion of the trench; and

performing a thermal treatment that causes migration of silicon material of the pillars toward the encapsulation layer to form the cavities and the thin film suspended over the cavities.

3. The method of claim 1, wherein forming the thin film comprises: and epitaxially growing the thin film.

4. The method of claim 1, wherein forming the via channel comprises: forming the plurality of holes through the conductive layer, the plurality of through holes having a first end in fluid communication with the external environment and a second end in fluid communication with the empty space above the thin film.

5. The method of claim 1, further comprising: filling the plurality of through holes with a filler layer; and wherein forming the fluid communication passage channel comprises:

forming a buried via channel contained within the substrate at a distance from the top surface and having a first opening in fluid communication with the cavity; and

wherein the substrate is a wafer, and wherein forming the cavity in the substrate comprises: forming a plurality of cavities in the wafer, the plurality of cavities forming thin films suspended over respective cavities, the method further comprising: sawing the wafer into a plurality of dies, each die comprising a cavity and a thin film.

6. The method of claim 1, wherein forming the via channel comprises: forming a buried via channel, the buried via channel being formed simultaneously with forming the cavity.

7. The method of claim 1, wherein the sensing capacitor is a first sensing capacitor, the method further comprising: a reference sensing capacitor is formed in the substrate.

8. A MEMS pressure sensor, comprising:

a body comprising a semiconductor material and having a top surface;

a fully enclosed buried cavity contained within the body and separated from the top surface by a membrane, wherein the membrane is suspended over the cavity;

a polysilicon layer suspended over the thin film and capacitively coupled to the thin film, the polysilicon layer separated from the thin film by a blank space;

a plurality of vias in the polysilicon layer, the plurality of vias configured to provide fluid communication between the membrane and an external environment;

a first electrical contact element coupled to the membrane; and

a second electrical contact element coupled to the polysilicon layer.

9. The sensor of claim 8, wherein the plurality of through-holes have a first end at the external environment and a second end at the empty space above the thin film.

10. The sensor of claim 8, wherein the first electrical contact element and the second electrical contact element are separated from each other by a separation trench.

11. The sensor of claim 8, wherein the sensor further comprises a reference structure in the body.

12. The sensor of claim 8, wherein the polysilicon layer and the thin film form a sensing capacitor, the capacitor further comprising a reference capacitor.

13. The sensor of claim 12, wherein the thin film is made of polysilicon.

14. An electronic device, comprising:

an ASIC; and

a MEMS pressure sensor coupled to the ASIC, the MEMS pressure sensor comprising:

a silicon body;

a fully enclosed buried cavity within the silicon body;

a membrane suspended over the cavity, the membrane formed from the silicon body;

a plate suspended above the membrane and separated from the membrane by a void space, the plate being made of a polysilicon material, the plate including a plurality of through holes fluidly coupling the membrane to an external environment;

a first electrical contact element coupled to the membrane; and

a second electrical contact element coupled to the plate, wherein the membrane and the plate form a sensing capacitor.

15. The electronic device defined in claim 14 wherein the plurality of vias have a first end in fluid communication with the external environment and a second end in fluid communication with the empty space above the thin film.

16. The electronic device of claim 14, wherein the electronic device is at least one of a smartphone, a tablet, a wearable device, and a smart watch.

17. A method for fabricating a MEMS pressure sensor, the method comprising:

forming a cavity in a substrate of silicon material;

forming a membrane suspended at the cavity;

forming a conductive layer of polysilicon, the conductive layer suspended over the membrane, a plate of the conductive layer separated from the membrane by a blank space;

forming a via channel providing fluid communication between the membrane and an external environment; and

forming electrical contact elements electrically coupled to the membrane and the plate, respectively, wherein the membrane and the plate form a sensing capacitor, wherein forming the electrical contact elements comprises:

forming a first contact trench through the conductive layer until reaching the sacrificial layer;

forming a second contact trench through the conductive layer and the sacrificial layer until reaching the top surface of the substrate;

forming a conductive region over the conductive layer and within the first and second contact trenches; and

the conductive area is defined by etching and a first electrical contact element of the membrane for electrical connection from the outside and a second electrical contact element of the plate for electrical connection from the outside are formed.

18. The method of claim 17, wherein the sensing capacitor is a first sensing capacitor, the method further comprising: a reference sensing capacitor is formed in the substrate.

19. The method of claim 17, wherein forming the thin film comprises: and epitaxially growing the thin film.

Technical Field

The present invention relates to a method for manufacturing a MEMS (micro electro mechanical system) pressure sensor and a corresponding MEMS pressure sensor.

Background

Integrated semiconductor pressure sensors manufactured using micromechanical technology (typically MEMS) are known.

These sensors are used, for example, within portable or wearable electronic devices, or in the automotive field, for example, for barometer applications.

In particular, piezoresistive pressure sensors are known, the operation of which is based on the piezoelectric resistivity, i.e. on the ability of some materials to modify their resistivity when they are subjected to a change when a mechanical stress is applied to them. For example, the resistivity decreases when compressive stress is applied, and increases when tensile stress is applied.

Piezoresistive pressure sensors typically include a membrane (or diaphragm) suspended over a cavity in a body of semiconductor material and undergoing deformation in the presence of an incoming pressure wave from the external environment.

Piezoresistive elements (typically constituted by implanted or diffused doped regions) are provided in the surface region of the membrane and are electrically connected to each other in a Wheatstone-bridge configuration.

The deformation of the membrane causes an imbalance of the wheatstone bridge, which can be detected by a specially provided electronic circuit, a so-called ASIC (application specific integrated circuit), coupled to the micromechanical structure of the sensor, which derives from said imbalance a value of the pressure acting on the membrane.

Even though these piezoresistive pressure sensors are widely and successfully used, the applicant has realised that they have some drawbacks at least for some applications.

In particular, the applicant has realised that sensors of this type generally have a non-linear response as a function of temperature, i.e. a high Thermal Coefficient (TCO). Further, the detection sensitivity depends on the temperature and generally deteriorates as the temperature increases.

Therefore, it may not be appropriate to use these sensors for applications that face high operating temperatures or generally wide temperature variations.

Furthermore, the manufacturing method is rather complex and expensive, since several implantation or diffusion masks are required, for example to obtain doped regions for forming piezoresistive elements within the thin film.

In addition, these piezoresistive sensors do not allow for the convenient implementation of a self-test flow for testing their normal function during operation.

In this connection, it is known that in some contexts, for example, applications in the automotive field, self-test capabilities of electronic systems are explicitly required in order to prevent errors and malfunctions.

Disclosure of Invention

The object of the present invention is to overcome, at least in part, the problems of MEMS pressure sensors of the known type, among which there are the ones that have been discussed previously.

According to the present invention, there is therefore provided a method for manufacturing a MEMS pressure sensor and a corresponding MEMS pressure sensor, as defined in the appended claims.

Drawings

For a better understanding of the invention, preferred embodiments thereof will now be described, by way of non-limiting example only, and with reference to the accompanying drawings, in which:

fig. 1 is a schematic cross-sectional view of a micromechanical structure of a MEMS pressure sensor in an initial step of a corresponding manufacturing method according to a first embodiment of the present solution;

fig. 2A is a schematic top plan view of the micromechanical structure in a subsequent step of the manufacturing method;

fig. 2B is a schematic cross-sectional view corresponding to the top plan view of fig. 2A;

figures 3-9 are schematic cross-sectional views of the micromechanical structure in subsequent steps of the manufacturing method;

figure 10 is a schematic top plan view of the micromechanical structure of figure 9;

fig. 11 is a schematic cross-sectional view of a micromechanical structure of a MEMS pressure sensor in a final step of a corresponding manufacturing method according to a second embodiment of the present solution;

figure 12 is a schematic top plan view of the micromechanical structure of figure 11;

fig. 13 is a schematic cross-sectional view of a micromechanical structure of a MEMS pressure sensor in a final step of a corresponding manufacturing method according to a third embodiment of the present solution;

figure 14 is a schematic top plan view of the micromechanical structure of figure 13;

figure 15 shows a graph comparing a plot of the temperature coefficient of a MEMS pressure sensor according to the present solution with a plot of the temperature coefficient of a piezoresistive pressure sensor of known type;

FIG. 16 is a general block diagram of an electronic device incorporating a MEMS pressure sensor in accordance with another aspect of the present technique; and

fig. 17 is a general block diagram of a variant embodiment of the MEMS pressure sensor.

Detailed Description

Referring first to fig. 1, a fabrication method for fabricating a capacitive type MEMS pressure sensor according to one embodiment of the present solution is now described.

In an initial step of the manufacturing method, a wafer 1 of semiconductor material (for example monocrystalline silicon) is provided, comprising for example a substrate 2 having an n-type (or equivalently p-type) doping and having a front surface 2a and a rear surface 2 b.

The manufacturing method continues with the formation of a buried cavity, completely contained within the wafer 1, covered by a thin film, using a technique such as that described in detail in EP 1324382B 1, filed in the name of the applicant.

As shown in fig. 2A and 2B (which, as with the other figures, are not necessarily drawn to scale), a first etch mask 3 is provided on a front surface 2A of the substrate 2, for example made of a photosensitive material (so-called "photoresist").

The first etch mask 3 defines (see enlarged detail of fig. 2A) an etch area which in this example is substantially square (but may equally be circular or generally polygonal) and comprises a plurality of mask portions 3a, for example hexagons, which define a crystal lattice, for example a honeycomb crystal lattice.

As will be apparent in the ensuing text, the etched area of the first etch mask 3 corresponds to the area to be occupied by the buried cavity and has an extension corresponding to the extension of the thin film to be formed over the same buried cavity.

Thereafter (see fig. 3, which is similar to fig. 2B, and represents only an enlarged portion of the wafer 1 for clarity of illustration), an anisotropic chemical etching of the substrate 2 is carried out, using the first etching mask 3, after which trenches 6 are formed which communicate with one another and define a plurality of pillars 7 made of silicon.

In practice, the trenches 6 form open areas of complex shape (corresponding to the crystal lattice of the first etch mask 3) in which pillars 7 (having a shape corresponding to the mask portions 3 a) extend.

Next, the first etching mask 3 is removed and epitaxial growth is performed in a deoxidation atmosphere (generally, in an atmosphere having a high hydrogen concentration, preferably in an atmosphere having trichlorosilane). Thus, an epitaxial layer grows over the pillars 7 and closes the above-mentioned open area formed by the trenches 6 at the top.

Thereafter, a step of thermal annealing is preferably carried out in a reducing atmosphere, typically in a hydrogen atmosphere, for example at 1190 ℃ for 30 minutes. The annealing step causes migration of silicon atoms, which tend to move into lower energy positions. Thus, also due to the short distance between the pillars 7, silicon atoms migrate entirely from the part of the pillars 7 present within the above-mentioned open region formed by the trenches 6, and from said region, a buried cavity 10 is formed.

As shown in fig. 4 (which represents an enlarged portion of the wafer 1 compared to fig. 2B and 3), a thin silicon layer remains above the buried cavity 10, partly consisting of epitaxially grown silicon atoms and partly consisting of migrated silicon atoms, and forms a thin film 12, the thin film 12 being flexible and capable of bending in the presence of external stresses.

In particular, the membrane 12 separates the buried cavity 10 from the top surface 2a of the substrate 2. The same buried cavity 10 is separated from the back surface 2b by a thick monolithic region of the substrate 2.

Advantageously, during the steps for forming the thin film 12 and the buried cavity 10, dopant atoms may be introduced into the substrate 2 and into the same thin film 12 in order to increase its electrical conductivity.

At the end of the steps of the manufacturing method that have been previously described, the buried cavity 10 is therefore formed within the substrate 2, is completely contained within the substrate 2, is separated from both the front surface 2a of the substrate 2 and from the rear surface 2b of the substrate 2 by a continuous portion of material. In other words, the buried cavity 10 does not have fluid communication with the outside of the substrate 2.

As shown in fig. 5, the manufacturing method is followed by the formation of a sacrificial layer 14, for example made of a dielectric material such as silicon oxide, on the top surface 2a of the substrate 2 and therefore on the membrane 12. The sacrificial layer 14 may be formed, for example, by means of a deposition technique on the entire wafer 1 (so-called "blank" deposition, without the use of a mask).

Next, a conductive layer 15 made of, for example, polysilicon is formed on the sacrificial layer 14. In this embodiment, a conductive layer 15 is epitaxially grown on the sacrificial layer 14 (again without using a mask).

Thereafter (fig. 6), through a second etch mask (not shown here), an etching of the conductive layer 15 is performed, wherein the etching stops on the sacrificial layer 14, causing a removal of material and forming a first pad trench 15 and a contact opening 17, both of which penetrate the conductive layer 15 in its thickness. The contact opening 17 is laterally arranged alongside the first pad trench 15 in a further outer position with respect to the film 12.

Next (fig. 7), the second etch mask is removed and a third etch mask (not shown here) is formed over the conductive layer 15, by means of which an etch of the sacrificial layer 14 is performed, wherein the etch stops on the substrate 2, thus removing the portion of the same sacrificial layer 14 perpendicular to the contact opening 17, in order to form the second pad trench 18.

The second pad groove 18 thus ends on the top surface 2a of the substrate 2 and is arranged alongside the first pad groove 16, in a laterally further outer position with respect to the film 12.

Next (fig. 8), the third etch mask is removed and a deposition mask (not shown herein) is formed on the conductive layer 15, which coats the conductive layer 15 at the region vertically corresponding to the thin film 12 and instead exposes the first and second pad trenches 16 and 18.

In the case of using the deposition mask, a metal region 20 of a suitable metal material, such as aluminum (or gold), is then deposited on the conductive layer 15.

In particular, this metal region 20 completely fills the first pad trench 16 and the second pad trench 18, contacting the top surface 2a of the substrate 2 within the second pad trench 18 and contacting the sacrificial layer 14 within the first pad trench 16, as shown in fig. 8.

Next (fig. 9), a fourth etching mask (not shown herein) is formed on the conductive layer 15 and the metal region 20, by which etching is performed, wherein the etching first stops on the sacrificial layer 14, which results in removing material and forming a plurality of holes 22, which holes 22 penetrate the conductive layer 15 in their thickness vertically in positions corresponding to the thin film 12 (for example, the holes 22 of the through type are formed according to a lattice arrangement as will be explained below).

Etching, e.g. chemical wet etching, is then continued in the underlying sacrificial layer 14 through the aperture 22, wherein the etching stops on the top surface 2a of the substrate 2, resulting in removal of material of the sacrificial layer 14 and formation of an empty space 24 above the membrane 12.

In particular, this empty space 24 places the membrane 12 in fluid communication with the external environment via the holes 22 through the conductive layer 15. The aperture 22 actually has a first end 22a in fluid communication with the ambient and a second end 22b in fluid communication with an empty space 24 above the membrane 12.

Through the same fourth etch mask, the etching (first of all the etching of the metal region 20 and of the conductive layer 15, and then of the sacrificial layer 14) results in the formation of a separation opening 29 which extends through the entire thickness of the metal region 20, of the conductive layer 15 and of the sacrificial layer 14 until reaching the top surface 2a of the substrate 2.

The partition opening 29 is provided in a position intermediate between the positions previously assumed by the above-described first pad trench 16 and second pad trench 18 and defines: starting with the conductive layer 15, the slab region 30 covering the empty space 24 and the film 12; and furthermore, starting from the metal region 20, two different pads 30a, 30b and in particular a first pad 30a arranged in contact with the substrate 2, constitute in its interior a second pad trench 18, and a second pad 30b arranged in contact with the plate region 30, constitutes in its interior a first pad trench 16.

The manufacturing method is then terminated by a step of sawing the wafer 1 to define dies 32, each die 32 comprising a body of semiconductor material 34 (constituted by a monolithic portion of the substrate 2 resulting from sawing the wafer 1), in which a micromechanical structure, indicated as a whole by 35, of the MEMS pressure sensor is integrated.

Fig. 10 is a schematic top plan view of the same micromechanical structure 35 at the end of the manufacturing method; the top plan view specifically shows a lattice (or array) arrangement of holes 22 made through the plate region 30.

In detail, the micromechanical structure 35 therefore comprises: a buried cavity 10, which is completely contained within a body of semiconductor material 34; and a thin film 12 disposed over the buried cavity 10 and separating the same buried cavity 10 from the top surface 2a of the body of semiconductor material 34; an empty space 24 above the membrane 12 that enables the membrane 12 to be deformed in the presence of an incoming pressure wave; a plate area 30 arranged vertically above the membrane 12, separated from the membrane 12 by empty spaces 24, wherein the corresponding holes 22 place the same empty spaces 24 (and the membrane 12) in communication with the environment outside the MEMS pressure sensor and thus enable the above-mentioned pressure waves to enter; and, in addition, a first pad 30a, which is in electrical contact with the body of semiconductor material 34 (and hence the film 12), and a second pad 30b, which is in electrical contact with the pad region 30.

In particular, the micromechanical structure 35 defines a sensing capacitor C (schematically illustrated in fig. 9) having a plate region 30 (thus constituted by an epitaxial polysilicon region released from the underlying substrate) as a first plate or electrode and a membrane 12 as a second plate, the first and second plates being separated by an empty space 24 (which constitutes the dielectric of the sensing capacitor C).

During operation, the pressure exerted by the external environment on the membrane 12 causes its deformation and a change in the capacitance of the sensing capacitor C. This capacitance change may be detected, for example, by a suitable ASIC of a MEMS pressure sensor designed to appropriately receive the capacitance change and process it (e.g., by amplification and filtering operations), through electrical connections to the first and second pads 30a, 30b to supply a sense signal indicative of the value of the detected pressure.

With reference to fig. 11 and 12, a second embodiment of a MEMS capacitive pressure sensor will now be described.

In this second embodiment, plate region 30 does not have apertures 22 for placing membrane 12 in fluid communication with the external environment; the same plate area 30 is actually constituted by a solid area without any openings.

In other words, the empty space 24 is in this case isolated from the external environment, enclosed between the plate region 30 on the top and the membrane 12 on the bottom (furthermore laterally delimited by the portion of the sacrificial layer 14 that remains after the chemical etching for releasing the plate region 30).

Indeed, applicants are aware that, at least in some applications, it may be disadvantageous to have the membrane 12 be directly fluid with the external environment. Indeed, it may be useful to protect the membrane 12 from contamination, impurities, and/or moisture.

In this case, the manufacturing method envisages that the holes 22 (again provided for freeing the plate region 30 by removal through chemical etching of the underlying sacrificial layer 14) are later filled by means of a step of thermal oxidation of the wafer 1, which results in the formation of a coating layer, indicated by 36 in fig. 11, on the exposed surface of the conductive layer 15. Specifically, the coating layer 36 completely fills the hole 22.

In this second embodiment, the fluid communication of the membrane 12 with the external environment to the body of semiconductor material 34 of the micromechanical structure 35 is ensured by a buried access channel 37, the buried access channel 37 being laterally connected up to the buried cavity 10 within the body of semiconductor material 34.

In particular, the buried via channel 37 extends at a depth parallel to the top surface of the body of semiconductor material 34 and has a first opening 37a in fluid communication with the buried cavity 10 and a second opening 37b in communication with the external environment at a side wall 34 'of the body of semiconductor material 34 (which side wall 34' extends perpendicular to the front and rear surfaces of the body of semiconductor material 34).

The buried via channel 37 is formed using the same method steps that result in the formation of the buried cavity 10.

In particular, the mask 3 (previously described with reference to fig. 2A and 2B) has in this case a lateral extension having the desired configuration for the buried via channel 37, and furthermore the step of sawing the wafer 1 is performed in such a way that the dicing lines define the above-mentioned second opening 37B of the buried via channel 37 in order to open the buried via channel 37 to the external environment.

In this second embodiment, the pressure wave thus enters the buried via channel 37 from the second opening 37b and impinges on the inner surface of the membrane 12 that is set in contact with the buried cavity 10, causing deformation of the membrane 12 and a change in capacitance of the sensing capacitor C (which is formed in a manner that is all similar to that described for the first embodiment except for this difference).

With reference to fig. 13 and 14, a third embodiment of a capacitive type MEMS pressure sensor will now be described.

In this third embodiment, the micromechanical structure 32 comprises a reference structure integrated in the same body of semiconductor material 34 in which a structure for detecting the pressure of the external environment is formed; the reference structure is designed to allow different types of pressure detection (i.e. having the property of invariance with respect to the pressure to be detected, with respect to a known pressure reference).

In this third embodiment, a pressure sensing structure, indicated by 38a, is provided in a manner entirely similar to the micromechanical structure 35 discussed in detail earlier with reference to fig. 9 and 10 (which has an aperture 22 through the plate region 30 to place the membrane 12 in fluid communication with the environment).

The reference structure, indicated by 38b, comprises a micromechanical structure, which is also entirely similar to the micromechanical structure 35, except that it does not comprise the buried cavity 10 and the membrane 12.

In particular, the reference structure 38b comprises: a respective plate region 30 'made of electrically conductive material, suspended above a surface portion 34a of a body 34 of semiconductor material set transversely with respect to the membrane 12 of the sensing structure 38a and separated from the same surface portion 34a by a respective empty space 24'; a plurality of respective apertures (22') through respective plate regions 30' for fluid communication of respective empty spaces 24' with an external environment; and respective substrates 30a ', 30b ' for the electrical connection of the above-mentioned surface portion 34a and the respective plate region 30' with the outside, which form a reference capacitor C_refThe plate of (1).

Capacitor C_refIs therefore not affected by the pressure to be detected (to the extent that the surface portion 34a of the body of semiconductor material 34 does not undergo deformation according to this pressure), and is instead affected by the same interference phenomena that damage the sensing structure 38a, for example in the presence of moisture.

The corresponding manufacturing method thus envisages entirely similar (simultaneously performed) method steps for providing the sensing structure 38a and the reference structure 38b, except for the absence of an initial step of forming a buried cavity for the reference structure 38 b.

The ASIC associated with the micromechanical structure receives in this case the sensing capacitor C and the reference capacitor C by means of the first pad 30a and the second pad 30b of the sensing structure 38a and by means of the similar first pad 30a 'and second pad 30b' of the reference structure 38b_refThe capacitance of both changes.

The ASIC advantageously handles the sensing capacitors in different waysC and a reference capacitor C_refIn order to eliminate the influence of disturbances, for example due to moisture, on the detected pressure value.

As shown in fig. 13, doped regions 39, 39 'may furthermore be present in both the sensing structure 38a and the reference structure 38b, in the surface portion of the body of semiconductor material 34 underneath the empty space 24, 24' (for the sensing structure 35a, set in a position corresponding to the thin film 12 and forming a surface portion of the same thin film 12).

The doped regions 39, 39' may be formed by implanting or diffusing dopants into a dedicated mask after forming the buried cavity 10, and in this case help to constitute the sensing and reference capacitors C, C_refA second plate of (a); advantageously, the presence of this doped region 39, 39' makes it possible to increase the conductivity of the above-mentioned second plate and improve the sensing characteristics.

The advantages of the described solution appear clearly from the foregoing description.

In particular, MEMS pressure sensors based on the principle of capacitive detection have a much lower variation and non-linearity with respect to temperature than known solutions based on the piezoresistive sensing principle.

In this regard, fig. 15 compares a plot of the temperature coefficient TCO (expressed as a percentage of the full scale FS) of a capacitive type MEMS pressure sensor according to the present solution with the temperature coefficient TCO' of a piezoresistive type of known pressure sensors.

From the comparison of the plots, the higher stability of the temperature of the MEMS pressure sensor according to the present solution is evident, as is the greater linearity of its response.

In particular, the applicant has found that for a temperature coefficient TCO' of 2 mbar/c (i.e. 0.2% FS/c) of the known pressure sensor, the temperature coefficient TCO of the MEMS pressure sensor according to the present solution is 0.4 mbar/c (i.e. 0.04% FS/c).

The method for manufacturing a MEMS pressure sensor according to the present solution is advantageously less complex and more expensive than the methods of pressure sensors of known type, in particular of piezoresistive type, due to the lack of masks dedicated to the methods of processing the diffusion of the corresponding piezoresistive elements.

In particular, the applicant has noted a reduction in the number of masks required by the manufacturing method, as for a method for manufacturing a piezoresistive pressure sensor requiring, for example, nine masks, the number of masks may be only five (four etching masks and one deposition mask) in the described embodiment.

In addition, the described solution advantageously enables a simple and efficient implementation of a self-test operation in a MEMS pressure sensor, for example by applying an appropriate electrical bias signal externally to the plate of the sensing capacitor C by means of the first and second pads 30a, 30 b. The above-mentioned characteristics are particularly advantageous, as highlighted previously, for example for applications in the automotive field.

In general, the above characteristics make the use of MEMS pressure sensors particularly advantageous in electronic devices 50, for example for barometer applications in the automotive field as schematically shown in fig. 16.

In particular, in fig. 16, the MEMS pressure sensor is denoted by 42, comprising the micromechanical structure 35 and the ASIC 43 described previously, which provide a corresponding reading interface (and may be provided in the same die 32 as that of the micromechanical structure 35 or in a different die, which may be housed in the same package in any case).

Electronic device 50 is generally capable of processing, storing, and/or transmitting and receiving signals and information, and includes: a microprocessor 44 that receives the signal detected by the MEMS pressure sensor 42; an input/output interface 45 connected to the microprocessor 44; and a non-volatile type of internal memory 46.

The electronic device 50, when used in the automotive field, can control, for example, the air/fuel mixture of the combustion in the engine or else the opening of the airbag as a function of the detected pressure value.

Finally, it is clear that modifications and variations may be made to what has been described and illustrated herein, without thereby departing from the scope of the present invention, as defined in the annexed claims.

In particular, it is clear that modifications can be made to the materials used to manufacture the MEMS pressure sensor 42, different metallic materials can for example be used to provide the pads 30a, 30b or else different dielectric materials for providing the sacrificial layer 14.

In addition, it is apparent that MEMS pressure sensor 42 may be advantageously used also for different applications where it is desirable to obtain detection of pressure having temperature independent characteristics in portable or wearable devices (e.g. smart phones, tablets, smart watches, etc.) or in industrial applications where high temperatures are reached (e.g. in the range from-40 ℃ to 175 ℃).

Furthermore, due to the compatibility of the manufacturing methods used, the MEMS pressure sensor may advantageously be integrated with another MEMS internal sensor and/or microphone.

In this connection, fig. 17 is a schematic illustration of a combined MEMS sensor, indicated by 62, comprising a micromechanical sensing structure of the combined type, indicated by 64, which advantageously integrates in the same body of semiconductor material a micromechanical structure 35, previously described in detail for pressure detection, and furthermore another micromechanical sensing structure 65 of a known type, for example for detecting accelerations, angular velocities or acoustic waves. The micromechanical structures 35, 65 are advantageously produced using all compatible production methods.

The combined MEMS sensor 62 also includes an ASIC, again indicated at 43, operatively coupled to the micromechanical mechanism 35 and to another micromechanical sensing mechanism 65, so as to provide a combined sensing structure (i.e., an accelerometer, gyroscope, or microphone combined with a pressure sensor).