Method for manufacturing a MEMS pressure sensor and corresponding MEMS pressure sensor

Abstract

Embodiments of the present disclosure relate to a method for manufacturing a MEMS pressure sensor and a corresponding MEMS pressure sensor. A method for manufacturing a MEMS pressure sensor with a micromechanical structure contemplates providing a wafer with a substrate of semiconductor material and a top surface; forming a buried cavity that is completely contained within the substrate and is separated from the top surface by a thin film hanging above the buried cavity; forming a fluid communication passage for fluid communication of the thin film with the external environment at a pressure whose value must be determined; forming a plate region made of a conductive material that is suspended above the thin film and is separated from the thin film by a blank space; and forming an electrical contact element for electrical connection of the thin film and the plate region, the electrical contact element being designed to form a plate of a sensing capacitor (C), the capacitance value of the sensing capacitor indicating the value of the pressure to be detected. In addition, a corresponding MEMS pressure sensor with a micromechanical structure is described.

Description

[0001] This application is a divisional application of the invention patent application with the application date of September 29, 2016, the application number of 201610868540.0, and the invention name of "Method for Manufacturing a MEMS Pressure Sensor and Corresponding MEMS Pressure Sensor". Technical Field

[0002] The present invention relates to a method for manufacturing a MEMS (Micro-Electro-Mechanical System) pressure sensor and a corresponding MEMS pressure sensor. Background Art

[0003] Integrated semiconductor pressure sensors manufactured using micromachining techniques (generally MEMS) are well known.

[0004] These sensors are used, for example, within portable or wearable electronic devices, or in the automotive field, for example, for barometer applications.

[0005] In particular, piezoresistive pressure sensors are well known, and their operation is based on piezoresistivity, that is, based on the ability of some materials to modify their resistivity when mechanical stress is applied to them to cause them to undergo changes. For example, the resistivity decreases when compressive stress is applied, and the resistivity increases when tensile stress is applied.

[0006] A piezoresistive pressure sensor generally includes a thin film (or diaphragm) that is suspended above a cavity in a body of semiconductor material and undergoes deformation in the presence of an incoming pressure wave from the external environment.

[0007] Piezoresistive elements (generally formed by implanted or diffused doped regions) are provided in the surface region of the thin film and are electrically connected to each other in a Wheatstone-bridge configuration.

[0008] The deformation of the thin film causes an imbalance in the Wheatstone bridge, which can be detected by a specifically provided electronic circuit (coupled to the micro-mechanical structure of the sensor), a so-called ASIC (Application Specific Integrated Circuit), which derives the value of the pressure acting on the thin film from said imbalance.

[0009] Even though these piezoresistive pressure sensors are widely and successfully used, the applicant has realized that they have some drawbacks at least for certain applications.

[0010] In particular, the applicant has realized that sensors of this type generally have a non-linear response according to temperature, that is, a high thermal coefficient (TCO). In addition, the detection sensitivity depends on temperature and generally deteriorates when the temperature increases.

[0011] Therefore, it may be inappropriate to use these sensors for applications facing high operating temperatures or generally wide temperature variations.

[0012] Furthermore, the manufacturing method is rather complex and expensive as several implantation or diffusion masks are required, for example, to obtain doped regions for forming piezoresistive elements within the thin film.

[0013] In addition, these piezoresistive sensors do not allow for the convenient implementation of a self - test procedure to test their normal functionality during operation.

[0014] In this regard, it is known that in some contexts of applications in, for example, the automotive field, a self - test capability of the electronic system is clearly required to prevent errors and malfunctions. Summary of the Invention

[0015] An object of the present invention is to overcome at least in part the problems of MEMS pressure sensors of the known type, among which are the problems previously discussed.

[0016] According to the present invention, there is thus provided a method for manufacturing a MEMS pressure sensor and a corresponding MEMS pressure sensor as defined in the appended claims. Brief Description of the Drawings

[0017] To better understand the present invention, the preferred embodiments of the present invention are now described by way of non - limiting examples only and with reference to the drawings, in which:

[0018] - Figure 1 is a schematic cross - sectional view of the micromechanical structure of a MEMS pressure sensor in an initial step of a corresponding manufacturing method according to a first embodiment of the present technical solution;

[0019] - Figure 2A is a schematic top plan view of the micromechanical structure in a subsequent step of the manufacturing method;

[0020] - Figure 2B is Figure 2A a schematic cross - sectional view corresponding to the top plan view of;

[0021] - Figures 3 - 9 is a schematic cross - sectional view of the micromechanical structure in a subsequent step of the manufacturing method;

[0022] - Figure 10 is Figure 9 a schematic top plan view of the micromechanical structure of;

[0023] - Figure 11 is a schematic cross - sectional view of the micromechanical structure of a MEMS pressure sensor in a final step of a corresponding manufacturing method according to a second embodiment of the present technical solution;

[0024] - Figure 12 is Figure 11 a schematic top plan view of the micromechanical structure of;

[0025] - Figure 13 is a schematic cross-sectional view of the micromechanical structure of a MEMS pressure sensor in a final step of a corresponding manufacturing method according to a third embodiment of the present technical solution;

[0026] - Figure 14 is Figure 13 a schematic top plan view of the micromechanical structure of;

[0027] - Figure 15 shows a graph comparing a plot of the temperature coefficient of a MEMS pressure sensor according to the present technical solution with a plot of the temperature coefficient of a piezoresistive pressure sensor of a known type;

[0028] - Figure 16 is an overall block diagram of an electronic device including a MEMS pressure sensor according to another aspect of the present technical solution; and

[0029] - Figure 17 is an overall block diagram of a variant embodiment of a MEMS pressure sensor. Detailed Description of the Invention

[0030] First, referring to Figure 1 , a manufacturing method for manufacturing a capacitive type MEMS pressure sensor according to an embodiment of the present technical solution will now be described.

[0031] In an initial step of the manufacturing method, a wafer 1 of semiconductor material (e.g., single-crystalline silicon) is provided, which includes a substrate 2 having, for example, an n-type (or equivalently p-type) doping and having a front surface 2a and a back surface 2b.

[0032] The manufacturing method continues with the formation of a buried cavity, which is fully contained within the wafer 1 and covered by a thin film, using a technique, for example, as detailed in EP 1 324382B1 filed in the name of the present applicant.

[0033] As Figure 2A and Figure 2B (like other attached Figure 1 drawings, which are not necessarily to scale) show, a first etch mask 3 is provided on the front surface 2a of the substrate 2 made of, for example, a photosensitive material (so-called "photoresist").

[0034] The first etch mask 3 defines (see Figure 2AThe enlarged detail) of the etched region, which is substantially square in this example (but could equally be circular or generally polygonal), and includes a plurality of mask portions 3a, such as hexagonal, which define a lattice, such as a honeycomb lattice.

[0035] As will become apparent in the following, the etched region of the first etch mask 3 corresponds to the region that will be occupied by the buried cavity and has an extent corresponding to the extent of the thin film that will be formed above the same buried cavity.

[0036] Afterwards (see the enlarged portion of the wafer 1 shown for clarity of illustration), using the first etch mask 3, an anisotropic chemical etch of the substrate 2 is performed, after which trenches 6 are formed, which communicate with each other and define a plurality of pillars 7 made of silicon. Figure 2B similar Figure 3 For the sake of clarity of illustration, only the enlarged portion of the wafer 1 is shown), using the first etch mask 3, an anisotropic chemical etch of the substrate 2 is performed, after which trenches 6 are formed, which communicate with each other and define a plurality of pillars 7 made of silicon.

[0037] In fact, the trenches 6 form an open area of a complex shape (corresponding to the lattice of the first etch mask 3), and the pillars 7 (having a shape corresponding to the mask portion 3a) extend therein.

[0038] Next, the first etch mask 3 is removed and epitaxial growth is performed in a deoxygenated environment (generally, in an environment with a high hydrogen concentration, preferably in an environment with trichlorosilane). Thus, an epitaxial layer grows above the pillars 7 and closes the above-mentioned open area formed by the trenches 6 at the top.

[0039] Afterwards, preferably in a reducing environment, generally in a hydrogen environment, for example, a thermal annealing step is performed at 1190 °C for 30 minutes. The annealing step causes the migration of silicon atoms, which tend to move to positions of lower energy. Therefore, also due to the short distance between the pillars 7, the silicon atoms completely migrate from the portions of the pillars 7 present in the above-mentioned open area formed by the trenches 6, and starting from said area, a buried cavity 10 is formed.

[0040] As Figure 4 (compared with Figure 2B and Figure 3 which shows an enlarged portion of the wafer 1), a thin silicon layer remains above the buried cavity 10, composed in part of epitaxially grown silicon atoms and in part of migrated silicon atoms, and forms a thin film 12, which is flexible and capable of bending in the presence of external stress.

[0041] In particular, the thin film 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 section of the substrate 2.

[0042] Advantageously, during the steps for forming the thin film 12 and the buried cavity 10, dopant atoms can be introduced into the substrate 2 and into the same thin film 12 in order to increase its conductivity.

[0043] At the end of the manufacturing method steps previously described, the buried cavity 10 is thus formed within the substrate 2, is completely contained within the substrate 2, and is separated from both the front surface 2a and the back 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 exterior of the substrate 2.

[0044] As Figure 5 shown, the manufacturing method then continues with the formation of a sacrificial layer 14 made of a dielectric material such as silicon oxide, for example, on the top surface 2a of the substrate 2 and thus on the thin film 12. The sacrificial layer 14 can be formed, for example, by means of a deposition technique (so-called "blank" deposition, without using a mask) over the entire wafer 1.

[0045] Next, a conductive layer 15 made of polysilicon, for example, is formed on the sacrificial layer 14. In this embodiment, the conductive layer 15 is epitaxially grown on the sacrificial layer 14 (likewise without using a mask).

[0046] Afterwards ( Figure 6 ), by means of a second etch mask (not shown herein), etching of the conductive layer 15 is performed, where the etching stops on the sacrificial layer 14, causing removal of material and formation of 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 disposed side by side with the first pad trench 15, in a more outward position relative to the thin film 12.

[0047] Next ( Figure 7 ), the second etch mask is removed and a third etch mask (not shown herein) is formed over the conductive layer 15, through which etching of the sacrificial layer 14 is performed, where the etching stops on the substrate 2, thus removing a portion of the same sacrificial layer 14 perpendicular to the contact opening 17 in order to form a second pad trench 18.

[0048] The second pad trench 18 thus ends on the top surface 2a of the substrate 2 and is disposed side by side with the first pad trench 16, in a more outward lateral position relative to the thin film 12.

[0049] Next ( Figure 8 ), the third etch mask is removed, and a deposition mask (not shown herein) is formed over the conductive layer 15, which coats the conductive layer 15 in the region corresponding vertically to the thin film 12 and instead exposes the first pad trench 16 and the second pad trench 18.

[0050] In the case of using this deposition mask, a metal region 20 of a suitable metal material (such as aluminum (or gold)) is then deposited on the conductive layer 15.

[0051] In particular, the metal region 20 completely fills the first pad trench 16 and the second pad trench 18, as Figure 8 shown, 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.

[0052] Next ( Figure 9 ), a fourth etching mask (not shown herein) is formed on the conductive layer 15 and the metal region 20, through which etching is performed, where the etching first stops on the sacrificial layer 14, which results in removing material and forming a plurality of holes 22, the plurality of holes 22 vertically penetrating the conductive layer 15 at positions corresponding to the thin film 12 in its thickness (for example, the through-type holes 22 are formed according to the lattice arrangement to be described below).

[0053] The etching, for example, chemical wet etching, then continues through the holes 22 in the underlying sacrificial layer 14, where the etching stops on the top surface 2a of the substrate 2, resulting in removing the material of the sacrificial layer 14 and forming a blank space 24 above the thin film 12.

[0054] In particular, the blank space 24 places the thin film 12 in fluid communication with the external environment via the holes 22 passing through the conductive layer 15. The holes 22 actually have a first end 22a in fluid communication with the external fluid and a second end 22b in fluid communication with the blank space 24 above the thin film 12.

[0055] Through the same fourth etching mask, the etching (first the etching of the metal region 20 and the conductive layer 15, and then the etching of the sacrificial layer 14) results in forming a partition opening 29 that penetrates the entire thickness of the metal region 20, the conductive layer 15, and the sacrificial layer 14 until reaching the top surface 2a of the substrate 2.

[0056] The partition opening 29 is set at an intermediate position between the positions previously presented by the above-mentioned first pad trench 16 and the second pad trench 18 and defines: starting from the conductive layer 15, a plate region 30 covering the blank space 24 and the thin film 12; and furthermore, starting from the metal region 20, two different pads 30a, 30b and in particular the first pad 30a set to contact the substrate 2, within which the second pad trench 18 is formed, and the second pad 30b set to contact the plate region 30, within which the first pad trench 16 is formed.

[0057] The manufacturing method then terminates with the step of sawing the wafer 1 to define the die 32, each die 32 including a body of semiconductor material 34 (constituted by a monolithic portion of the substrate 2 obtained from the sawed wafer 1), and a micromechanical structure generally designated by 35 is integrated in the body.

[0058] Figure 10 is a schematic top plan view of the same micromechanical structure 35 at the end of the manufacturing method; this top plan view specifically shows the lattice (or array) arrangement of the holes 22 made through the plate region 30.

[0059] Specifically, the micromechanical structure 35 thus includes: a buried cavity 10, which is completely contained within the body made of semiconductor material 34; and a thin film 12, which is disposed above the buried cavity 10 and separates the same buried cavity 10 from the top surface 2a of the body of semiconductor material 34; a blank space 24 above the thin film 12, which enables the thin film 12 to deform in the presence of an incoming pressure wave; a plate region 30 disposed vertically above the thin film 12, separated from the thin film 12 by the blank space 24, where corresponding holes 22 put the same blank space 24 (and the thin film 12) in communication with the environment external to the MEMS pressure sensor and thus enable the above-mentioned pressure wave to enter; and furthermore, a first pad 30a, which is in electrical contact with the body of semiconductor material 34 (and thus the thin film 12), and a second pad 30b, which is in electrical contact with the plate region 30.

[0060] In particular, the micromechanical structure 35 defines a sensing capacitor C (schematically shown in Figure 9 ), which has the plate region 30 as the first plate or electrode (thus constituted by an epitaxial polysilicon region released from the underlying substrate) and the thin film 12 as the second plate, and the first plate and the second plate are separated by the blank space 24 (which constitutes the dielectric of the sensing capacitor C).

[0061] During operation, the pressure applied by the external environment on the thin film 12 causes its deformation and a change in the capacitance of the sensing capacitor C. This change in capacitance can be detected, for example, by a suitable ASIC of the MEMS pressure sensor designed to appropriately receive the capacitance change and process it (e.g., through amplification and filtering operations) via electrical connections to the first pad 30a and the second pad 30b to supply a sensing signal indicating the value of the detected pressure.

[0062] Referring to Figure 11 and Figure 12 , a second embodiment of the MEMS capacitive pressure sensor will now be described.

[0063] In this second embodiment, the plate region 30 does not have holes 22 for placing the membrane 12 in fluid communication with the external environment; the same plate region 30 is in fact constituted by a solid region without any openings.

[0064] In other words, the void space 24 is in this case isolated from the external environment and is enclosed between the top plate region 30 and the bottom membrane 12 (moreover, it is laterally delimited by the part of the sacrificial layer 14 remaining after the chemical etching for releasing the plate region 30).

[0065] In fact, the Applicant has realized that in at least some applications, putting the membrane 12 in direct fluid communication with the external environment may be disadvantageous. In fact, it may be useful to protect the membrane 12 from contamination, impurities, and / or moisture.

[0066] In this case, the manufacturing method envisages that the holes 22 (again provided for releasing the plate region 30 by removal via 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 Figure 11 represented by 36 on the exposed surface of the conductive layer 15. Specifically, this coating layer 36 completely fills the holes 22.

[0067] In this second embodiment, the fluid communication between the membrane 12 and the external environment of the body of the semiconductor material 34 of the micromechanical structure 35 is ensured by a buried access channel 37, which is laterally and upwardly connected to a buried cavity 10 within the body of the semiconductor material 34.

[0068] In particular, the buried access channel 37 extends at a depth parallel to the top surface of the body of the 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 the side wall 34' of the body of the semiconductor material 34 (this side wall 34' extends perpendicular to the front and rear surfaces of the body of the semiconductor material 34).

[0069] The buried access channel 37 is formed using the same method steps that result in the formation of the buried cavity 10.

[0070] In particular, the mask 3 (previously referred to Figure 2A and Figure 2B described) in this case has a laterally extended portion that has the desired configuration for the buried access channel 37, and moreover, 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 access channel 37 in order to open the buried access channel 37 to the external environment.

[0071] In this second embodiment, the pressure wave thus enters the buried channel 37 from the second opening 37b and impinges on the inner surface of the thin film 12 that is set to contact the buried cavity 10, causing deformation of the thin film 12 and a change in the capacitance of the sensing capacitor C (except for this difference, it is formed in a manner entirely similar to that described for the first embodiment).

[0072] Reference Figure 13 and Figure 14 , a third embodiment of a capacitive type MEMS pressure sensor will now be described.

[0073] In this third embodiment, the micromechanical structure 32 includes a reference structure that is integrated in the same body of the semiconductor material 34 in which the 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 characteristic of invariance with respect to the pressure to be detected relative to a known pressure reference).

[0074] In this third embodiment, the pressure sensing structure represented by 38a is provided in a manner entirely similar to the micromechanical structure 35 previously referenced Figure 9 and Figure 10 and discussed in detail (which has holes 22 through the plate region 30 to put the thin film 12 in fluid communication with the outside).

[0075] The reference structure represented by 38b includes a micromechanical structure that is entirely similar to the micromechanical structure 35 except that it does not include the buried cavity 10 and the thin film 12.

[0076] Specifically, the reference structure 38b includes: a corresponding plate region 30', which is made of a conductive material, is suspended above the surface portion 34a of the body of the semiconductor material that is set laterally with respect to the thin film 12 of the sensing structure 38a and is separated from the same surface portion 34a by a corresponding blank space 24'; a plurality of corresponding holes (22') through the corresponding plate region 30' for fluid communication between the corresponding blank space 24' and the external environment; and corresponding substrates 30a', 30b' for the electrical connection of the above surface portion 34a and the corresponding plate region 30' to the outside, which form the plates of the reference capacitor C ref of.

[0077] The capacitor C ref The capacitance value of is thus not affected by the pressure to be detected (to the extent that the surface portion 34a of the body of the semiconductor material 34 does not undergo deformation according to this pressure), and instead is affected by the same interference phenomena that, for example, damage the sensing structure 38a in the presence of moisture.

[0078] The corresponding manufacturing method thus envisages providing completely similar (simultaneous) method steps for the sensing structure 38a and the reference structure 38b, except for the initial step of forming the buried cavity for the reference structure 38b being missing.

[0079] The ASIC associated with the micromechanical structure in this case receives the sensing capacitor C and the reference capacitor C by means of the first pads 30a and 30b of the sensing structure 38a and by means of the similar first pads 30a' and second pads 30b' of the reference structure 38b ref of the capacitance changes of both.

[0080] The ASIC advantageously processes the sensing capacitor C and the reference capacitor C in different ways ref of these capacitance changes in order to eliminate, for example, the influence of interference due to moisture on the detected pressure value.

[0081] As Figure 13 shown, doping regions 39, 39' may furthermore be present in both the sensing structure 38a and the reference structure 38b, in the surface portions of the body of the semiconductor material 34 below the blank spaces 24, 24' (for the sensing structure 35a, being set in the position corresponding to the thin film 12 and forming the surface portion of the same thin film 12).

[0082] The doping 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 contribute to constituting the second plates of the sensing capacitor C and the reference capacitor C ref ; advantageously, the presence of the doping regions 39, 39' enables an increase in the conductivity of the above-mentioned second plates and an improvement in the sensing characteristics.

[0083] The advantages of the described technical solution clearly emerge from the foregoing description.

[0084] In particular, a MEMS pressure sensor based on the principle of capacitance detection has much lower temperature variations and non-linearity relative to temperature than known technical solutions based on the piezoresistive sensing principle.

[0085] At this point, Figure 15 a plot of the temperature coefficient TCO (expressed as a percentage of the full scale FS) of a capacitance-type MEMS pressure sensor according to the present technical solution is compared with the temperature coefficient TCO' of a known piezoresistive-type pressure sensor.

[0086] From the comparison of the plots, the higher stability of the temperature of the MEMS pressure sensor according to the present technical solution is evident, as is the greater linearity of its response.

[0087] Specifically, the applicant has found that, for a temperature coefficient TCO' of 2 mbar / °C (i.e., 0.2% FS / °C) for a known pressure sensor, the temperature coefficient TCO of the MEMS pressure sensor according to the present technical solution is 0.4 mbar / °C (i.e., 0.04% FS / °C).

[0088] Due to the lack of a mask for the method dedicated to processing the diffusion of the corresponding piezoresistive element, the method for manufacturing a MEMS pressure sensor according to the present technical solution is advantageously less complex and expensive than the methods for pressure sensors of known types (specifically piezoresistive types).

[0089] In particular, the applicant has noted a reduction in the number of masks required by the manufacturing method. For example, for a method for manufacturing a piezoresistive pressure sensor that requires nine masks, the number of masks can be only five (four etching masks and one deposition mask) in the described embodiments.

[0090] In addition, the described technical 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 to the plates of the sensing capacitor C from the outside via the first pad 30a and the second pad 30b. The above characteristics are particularly advantageous, as previously emphasized, for applications in the automotive field, for example.

[0091] Generally, the above characteristics make the use of a MEMS pressure sensor in an electronic device 50 particularly advantageous, for example, for Figure 16 the barometer applications in the automotive field schematically shown in

[0092] In particular, in Figure 16 the MEMS pressure sensor is represented by 42 and includes the previously described micro-mechanical structure 35 and the ASIC 43, which provides a corresponding read interface (and can be provided in the same die 32 as the die of the micro-mechanical structure 35 or in a different die, which can in any case be housed in the same package).

[0093] The 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 signals detected by the MEMS pressure sensor 42; an input / output interface 45 connected to the microprocessor 44; and an internal memory 46 of non-volatile type.

[0094] When used in the automotive field, the electronic device 50 can control, for example, the air / fuel mixture for combustion in the engine or otherwise control the deployment of the airbag according to the detected pressure value.

[0095] 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 invention as defined in the appended claims.

[0096] Specifically, it is obvious that the materials used to manufacture the MEMS pressure sensor 42 can be modified, and different metal materials can be used, for example, to provide the pads 30a, 30b or else different dielectric materials can be used to provide the sacrificial layer 14.

[0097] In addition, it is obvious that the MEMS pressure sensor 42 can also be advantageously used in different applications where it is desired to obtain a pressure detection with temperature-independent characteristics in a portable or wearable device (such as a smartphone, a tablet, a smartwatch, etc.) or in an industrial application where high temperatures (for example, in the range from -40 °C to 175 °C) are reached.

[0098] Furthermore, due to the compatibility of the manufacturing methods used, the MEMS pressure sensor can be advantageously integrated with another MEMS internal sensor and / or microphone.

[0099] At this point, Figure 17 is a schematic illustration of a combined MEMS sensor represented by 62, including a micromachined sensing structure of the type represented by 64, which advantageously integrates the micromachined structure 35 described in detail previously for pressure detection and, in addition, another micromachined sensing structure 65 of a known type, for example, for detecting acceleration, angular velocity or acoustic waves, in the same body of semiconductor material. The micromachined mechanisms 35, 65 are advantageously fabricated using all compatible manufacturing methods.

[0100] The combined MEMS sensor 62 also includes an ASIC, again represented by 43, which is operatively coupled to the micromachined mechanism 35 and coupled to another micromachined sensing mechanism 65 in order to provide a combined sensing structure (i.e., an accelerometer, a gyroscope, or a microphone combined with a pressure sensor).

Claims

1. A method for manufacturing a MEMS pressure sensor, the method comprising: Form a completely enclosed buried cavity in a silicon material substrate; Form a thin film suspended at the buried cavity; Form a conductive layer suspended above the thin film, the conductive layer including a plate separated from the thin film by a blank space, the plate being made of polysilicon, wherein forming the plate includes: A sacrificial layer at the top surface of the substrate; Grow the conductive layer on the sacrificial layer; Form a plurality of through holes in the conductive layer; and Partially remove the sacrificial layer through the plurality of through holes and release a portion of the conductive layer relative to the substrate, wherein partially removing the sacrificial layer forms the plate and the blank space above the thin film; Form a via channel, wherein the plurality of through holes are components of the via channel, and the via channel provides fluid communication between the thin film and the external environment; and Form electrical contact elements electrically coupled to the thin film and the plate respectively, wherein the thin film and the plate form a sensing capacitor, wherein forming the electrical contact elements includes: Form a first contact trench that penetrates the conductive layer until reaching the sacrificial layer; Form a second contact trench that penetrates the conductive layer and the sacrificial layer until reaching the top surface of the substrate; Form a metal region above the conductive layer and within the first contact trench and the second contact trench; and Define the metal region by etching and form a first electrical contact element for electrical connection from the outside to the thin film and a second electrical contact element for electrical connection from the outside to the plate.

2. The method according to claim 1, wherein forming the buried cavity comprises: Form a trench at the top surface within the substrate, the trench being defined by pillars of the substrate; Epitaxially grow a closed layer of silicon material at the pillars, the closed layer closing the trench at the top portion of the trench; And Perform a heat treatment that causes migration of the silicon material of the pillars towards the closed layer to form the buried cavity and the thin film suspended above the buried cavity.

3. The method according to claim 1, wherein forming the thin film comprises: Epitaxially grow the thin film.

4. The method according to claim 1, wherein forming the via channel comprises: Form the plurality of through holes that penetrate 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 blank space above the thin film.

5. The method according to claim 1, wherein the sensing capacitor is a first sensing capacitor, and the method further comprises: Form a reference sensing capacitor in the substrate.

6. A MEMS pressure sensor, comprising: A body, including a semiconductor material and having a top surface; A micro - mechanical structure, including: A completely enclosed buried cavity contained within the body and separated from the top surface by a thin film, wherein the thin film is suspended above the buried cavity; A polysilicon layer suspended above the thin film and capacitively coupled to the thin film, the polysilicon layer being separated from the thin film by a blank space; A plurality of through holes in the polysilicon layer configured to provide fluid communication between the thin film and the external environment; A first electrical contact element coupled to the thin film; and A second electrical contact element coupled to the polysilicon layer.

7. The sensor according to claim 6, wherein the plurality of through holes have a first end at the external environment and a second end at the blank space above the thin film.

8. The sensor according to claim 6, wherein the first electrical contact element and the second electrical contact element are separated from each other by a separation trench.

9. The sensor according to claim 6, wherein the sensor further comprises a reference structure in the body, the reference structure corresponding to the micro-mechanical structure but without a buried cavity and a thin film.

10. The sensor according to claim 6, wherein the polysilicon layer and the thin film form a sensing capacitor, and the sensing capacitor further comprises a reference capacitor.

11. The sensor according to claim 10, wherein the thin film is made of polysilicon.

12. An electronic device, comprising: 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 thin film suspended above the buried cavity, the thin film formed from the silicon body; A plate suspended above the thin film and separated from the thin film by a void space, the plate made of a polysilicon material, the plate including a plurality of through holes that fluidically couple the thin film to the external environment; A first electrical contact element coupled to the thin film; and A second electrical contact element coupled to the plate, wherein the thin film and the plate form a sensing capacitor.

13. The electronic device according to claim 12, wherein the plurality of through holes have a first end in fluid communication with the external environment and a second end in fluid communication with the blank space above the thin film.

14. The electronic device according to claim 12, wherein the electronic device is at least one of a smart phone, a tablet computer, and a wearable device.

15. A method for manufacturing a MEMS pressure sensor, the method comprising: Form a fully enclosed buried cavity in a substrate of silicon material; Form a thin film suspended at the buried cavity; Form a conductive layer of polysilicon suspended above the thin film, the plate of the conductive layer separated from the thin film by a void space; Form a via channel including: forming the plurality of through holes through the conductive layer as part of the via channel, wherein the via channel provides fluidic communication between the thin film and the external environment; and Form electrical contact elements electrically coupled to the thin film and the plate respectively, wherein the thin film and the plate form a sensing capacitor, wherein forming the electrical contact elements includes: Form a first contact trench that passes through the conductive layer until it reaches a sacrificial layer; Form a second contact trench that passes through the conductive layer and the sacrificial layer until it reaches the top surface of the substrate; Form a metal region above the conductive layer and within the first contact trench and the second contact trench; and Define the metal region by etching and form a first electrical contact element for electrical connection from the outside to the thin film and a second electrical contact element for electrical connection from the outside to the plate.

16. The method according to claim 15, wherein the sensing capacitor is a first sensing capacitor, and the method further comprises: Form a reference sensing capacitor in the substrate.

17. The method according to claim 15, wherein forming the thin film comprises: Epitaxially grow the thin film.

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