Process for manufacturing a microelectromechanical device and MEMS device

Abstract

Embodiments of the present disclosure relate to processes for manufacturing microelectromechanical devices and MEMS devices. A process for manufacturing a MEMS device includes forming a first structural layer of a first thickness on a substrate. First trenches are formed through the first structural layer, and mask regions separated by first openings are formed on the first structural layer. A second structural layer of a second thickness is formed on the first structural layer that is in direct contact with the first structural layer at the first openings, and the second structural layer and the first structural layer together form a thick structural region of a third thickness, the third thickness being equal to the sum of the first thickness and the second thickness. A plurality of second trenches are formed through the second structural layer above the mask regions, and third trenches are formed through the first structural layer and the second structural layer by removing a selective portion of the thick structural region.

Description

Technical Field

[0001] The present disclosure relates to a process for manufacturing microelectromechanical (MEMS) devices, and more particularly to a mobile sensor and its MEMS device that utilize capacitance control / detection. Background Art

[0002] Specifically, the MEMS devices considered include two stacked structural layers that form at least one structure (a so-called "in-plane" or "out-of-plane" mobile structure) that is movable in-plane or out-of-plane within the plane of one of the structural layers; the movable structure can be, for example, a Z-detection sensor and has a first mass or a first movable electrode formed in one of the structural layers that is tiltable about a horizontal axis and is capacitively coupled to a second mass or a second fixed electrode formed in the other structural layer.

[0003] Specifically, in the following description, the MEMS mobile sensor and its manufacturing problems will be referred to; however, the present disclosure is generally applicable to other types of MEMS devices.

[0004] For example, the MEMS device can include one or more of the following structures, which can be a single structure or coupled to each other (a combination): an accelerometer, a gyroscope, a geophone, an inclinometer, and a resonator. In addition, the MEMS device can be a MEMS actuator.

[0005] This type of micro-mechanical device is widely used in consumer, automotive, and industrial applications.

[0006] As is known, during the design of this type of device, several aspects need to be considered, the most relevant of which are:

[0007] 1) Reducing the device size in order to reduce the manufacturing cost and improve the integration of the device into portable devices, such that the device has a very low footprint in both cost and volume;

[0008] 2) Sensitivity improvement, i.e., in the case of an actuator, a high ratio between the change in the detected signal and the trend of the monitored physical quantity (acceleration / rotation), i.e., a high ratio between the movement performed and the control signal;

[0009] 3) Performance stability in the case of mechanical stress due to packaging, soldering processes, or temperature;

[0010] 4) Mechanical strength in the case of drops and impacts.

[0011] Today, this type of device is manufactured using different types of technology. For example, the applicant has developed a technology that includes growing a thick epitaxial layer (which is the structural layer that houses the detection or actuation structures) above a sacrificial layer, and the sacrificial layer is removed using hydrofluoric acid vapor at the end of the manufacturing process.

[0012] Figure 1 and Figure 2 For example, a general MEMS sensor 1 is shown, which can be obtained using this process, and the process includes: forming a dielectric layer (which partially forms an insulating layer 3) on a substrate 2 such as single-crystalline silicon; forming a conductive region 4 (forming electrodes and interconnects) on the dielectric layer; growing a sacrificial layer above the dielectric layer and the conductive region 4 (a part of which is visible in Figure 1 and forms an insulating layer 3 together with the dielectric layer); etching the sacrificial layer where it is desired to form an anchoring element to the substrate 2; performing polysilicon epitaxial growth to form an anchor 5 and a structural layer 6; performing dry silicon etching to define a MEMS structure 7 in the structural layer; and selectively etching the sacrificial layer to release the movable elements of the MEMS structure 7. For example, Figure 2 shows a structure of a first fixed electrode 8A and a second fixed electrode 8B (usually indicated by 8 in Figure 1 ), and an interdigital movable electrode 9, which forms a MEMS structure 7, here a capacitance detection structure.

[0013] Generally, the process also includes final steps, including forming a metal connection region 10 and bonding a cover 11 through a bonding layer 12 (such as glass powder).

[0014] Specifically, the cover 11 can also be formed of semiconductor material by a processed silicon wafer to have auxiliary structures. For example, in Figure 1 , the cover 11 is recessed at the electrodes 8A, 8B and 9 and has a protruding portion 14 that points to the MEMS structure 7 and forms a vertical movement stopper (so-called Z-stopper) of the MEMS structure 7.

[0015] The cover 11 has a sealing and airtight function, and its purpose is to protect the MEMS structure 7 from the external environment (moisture, dust, etc.) and impacts. Its formation from a semiconductor wafer allows the use of back-end processing technologies such as testing, dicing, and packaging, and allows obtaining uniform performance and durability of the packaged device over time.

[0016] The process described above has been allowed to manufacture inertial devices with high electrical, mechanical, and reliability characteristics, especially mobile sensors (such as accelerometers, gyroscopes), at a reduced cost, which has determined its significant commercial success but is susceptible to improvement.

[0017] For example, the effectiveness and operability of the vertical stopper (protrusion 14) are related to the thickness of the bonding layer 12 (usually 5 to 7 μm), which is optimized with respect to the bonding function of the bonding layer 12, and thus is not always optimized with respect to the limitation of the desired vertical movement.

[0018] In addition, this solution does not allow two detection structures to be riveted in the same packaging device. Therefore, when using devices of the packaging device that use different types or multiple devices intended for detection on different axes, the various devices are arranged adjacent to each other on a support (such as a plate) or stacked on top of each other, resulting in space occupation.

[0019] Furthermore, the possibility of restricting the vertical (out-of-plane) movement of the MEMS structure 7 due to implementation considerations not related to the stop function is limited by the thickness of the bonding layer 12, and thus is not always optimized with respect to the desired value of the allowed movement.

[0020] Patent application US 2013 / 0043548 describes a manufacturing process that includes: forming a first polysilicon micromachined functional layer above a first insulating layer extending on a substrate, and then the first polysilicon micromachined functional layer is patterned to form defined trenches whose size can subsequently be filled with a second insulating layer, and forming a pillar structure. Then, a portion of the first micromachined functional layer disposed between the pillar structures is selectively removed to form cavities; a third insulating layer that is selectively removed to locally expose contact areas is formed above the remaining portion of the first micromachined functional layer (including the contact areas) and the remaining portion of the pillar structure. Then, a second micromachined functional layer is formed and is in direct electrical contact with the contact areas where the second insulating layer has been removed. Then, the second micromachined functional layer is defined to form access openings leading to the underlying layer; finally, the third insulating layer, the second insulating layer, the pillar structure, and the first insulating layer are selectively removed.

[0021] However, since the height of the first micromachined functional layer is limited by the ability of the pillar structure to support the second micromachined functional layer above the cavities and the criticality of the pillar structure itself (the width is reduced (due to the width of the trenches fabricated therein)), this process is also limited. In fact, as emphasized in this document, the trenches in which the pillar structures are formed need to be very thin, which may lead to filling difficulties, and due to the formation of defective pillar structures, it may result in removing polysilicon portions from the areas where they should exist during the selective removal process of the first polysilicon, and depositing polysilicon in defective trenches in undesired areas. In addition, the thinness of the pillar structure limits its height. Summary of the Invention

[0022] In various embodiments, the present disclosure provides solutions to overcome the disadvantages of the prior art.

[0023] According to the present disclosure, a process for manufacturing a MEMS device and a MEMS device are provided.

[0024] In at least one embodiment, a process for manufacturing a MEMS device is provided, including: forming a first structural layer of semiconductor material on a substrate, the first structural layer having a first thickness; forming a plurality of first trenches extending through the first structural layer and defining a first functional element; forming mask regions on the first structural layer, the mask regions being separated from each other by first openings; forming a second structural layer of semiconductor material on the first structural layer and the mask regions, the second structural layer having a second thickness, the second structural layer being in direct contact with the first structural layer at the first openings and together with the first structural layer forming a thick structural region of semiconductor material having a third thickness, the third thickness being equal to the sum of the first thickness and the second thickness; forming a plurality of second trenches extending through the second structural layer above the mask regions; and forming a plurality of third trenches extending through the first structural layer and the second structural layer by removing a selective portion of the thick structural region.

[0025] In at least one embodiment, a MEMS device including a substrate is provided. The first structural layer has a first thickness and extends on the substrate. The second structural layer has a second thickness and extends on the first structural layer. A plurality of first trenches extend through the first structural layer and define a first functional element. A plurality of second trenches extend through the second structural layer and define a second functional element covering the first functional element. A plurality of third trenches extend through the first structural layer and the second structural layer. The first structural layer and the second structural layer form a support structure having a third thickness equal to the sum of the first thickness and the second thickness, the support structure being anchored to the substrate and supporting the first functional element and the second functional element. A first gap region extends between the first functional element and the second functional element and surrounds the support structure.

[0026] In at least one embodiment, a method is provided, including: forming a plurality of first trenches extending through a first semiconductor layer and defining a first functional element, the first semiconductor layer having a first thickness; forming mask regions on the first semiconductor layer, the mask regions being separated from each other by openings; forming a second semiconductor layer on the first semiconductor layer and the mask regions, the second semiconductor layer being in direct contact with the first semiconductor layer at the openings; forming a plurality of second trenches extending through the second semiconductor layer and at least partially exposing portions of the mask regions; forming a cavity and a plurality of third trenches by selectively removing portions of the second semiconductor layer, the cavity covering at least one of the mask regions, the plurality of third trenches extending from the cavity through the second semiconductor layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To better understand the present disclosure, its embodiments are now described by way of non-limiting examples only with reference to the accompanying drawings, in which:

[0028] Figure 1 is a cross-sectional view of a known capacitive MEMS sensor;

[0029] Figure 2 is Figure 1 a perspective view of a sensor of

[0030] Figure 3 is a cross-sectional view of an embodiment of the present MEMS device;

[0031] Figures 4 to 12 is a cross-sectional view of a semiconductor wafer in successive steps of a MEMS device for fabricating Figure 3 according to an embodiment;

[0032] Figure 13A and Figure 13B illustrate Figure 3 different embodiments of a portion of a MEMS device of

[0033] Figures 14 to 16 illustrates variations of steps of Figures 10 to 12 according to the present process. DETAILED DESCRIPTION

[0034] Figure 3 illustrates a MEMS device 30 including a substrate 31; an insulating layer 32 above the substrate 31; a conductive region 33 above the insulating layer 32 and partially within the insulating layer 32; a first micromachined structure 35, here a differential sensor for out-of-plane movement (e.g., a Z-accelerometer or gyroscope having pitch and roll movement), the first micromachined structure 35 having a pair of upper electrodes 36A, 36B and a pair of bottom electrodes 37A, 37B; a Z-stopper structure 38; a second micromachined structure 40, e.g., a gyroscope or accelerometer with reduced thickness; and a lid 44 attached to a fixed portion 45 of the MEMS device 30 by an adhesive layer 46.

[0035] The first micromachined structure 35 and the second micromachined structure 40, the Z-stopper structure 38 and the fixed portion 45 are formed from two epitaxial layers (a first epitaxial layer 41 and a second epitaxial layer 42) grown epitaxially on one another, as described in detail below with reference to Figures 4 to 15 below.

[0036] Figure 4 illustrates a wafer 50, which includes a substrate 31 of semiconductor material, such as single-crystalline silicon; a first dielectric layer 51, such as silicon oxide, extending above the substrate 31; a conductive region 33, such as deposited polysilicon, extending above the first dielectric layer 51; a first sacrificial layer 53, such as thermally grown or deposited silicon oxide, extending above the conductive region 33 and the first dielectric layer 51; and a first epitaxial layer 41 of silicon above the first sacrificial layer 53.

[0037] Above the conductive region 33, the first sacrificial layer 53 has a first anchor opening 55 formed through a masking and etching step and accommodating an anchor portion 56 formed of the first epitaxial layer 41. The anchor portion 56 also forms the electrical contacts and biasing structures of the microelectromechanical structures 35, 40 and any other regions and structures of the MEMS device 30.

[0038] The first epitaxial layer 41 has a thickness associated with the desired microelectromechanical structure, which can be in the range between, for example, 2 and 80 μm. After epitaxial growth, the first epitaxial layer 41 is planarized and, for example, reaches the desired final thickness by CMP (chemical mechanical polishing).

[0039] In Figure 5 , the first epitaxial layer 41 is etched to define the lower part of the desired structure and other expected regions. For this purpose, the wafer 50 is covered with a resist mask (first trench mask), not shown, and subjected to dry etching, thereby forming a first trench 58 extending through the first epitaxial layer 41. The first trench 58 is thin with a minimum width (e.g., 2 μm). The etching automatically stops on the first sacrificial layer 53 and, here, defines the bottom electrodes 37A, 37B and the electrodes of the second microelectromechanical structure 40 and other structures. Specifically, in this step, the trench (indicated by 58') for defining the first Z stopper structure 38 and any other regions that may not be (at least completely) implemented through the second epitaxial layer 42 are formed.

[0040] Then, Figure 6 , a second sacrificial layer 60, such as TEOS (tetraethyl orthosilicate), is deposited, the thickness of which is included between, for example, 1 and 2 μm. The second sacrificial layer 60 partially fills the first trench 58, for example, by one third of the depth of the first trench 58 (e.g., 5 to 10 μm), although this filling and the degree and depth of filling are not important. Then, the second sacrificial layer 60 is planarized.

[0041] In Figure 7 , the second sacrificial layer 60 is thinned, where a portion where the second epitaxial layer 42 projects downward or the distance from the first epitaxial layer 41 is reduced is required, as described below. For this purpose, mask etching (e.g., time etching) is performed in a known manner by using a mask layer (bump mask), not shown, to form a groove 61. Here, the groove 61 extends, for example, above the bottom electrodes 37A, 37B, where the distance between the bottom electrodes 37A, 37B and the upper electrodes 36A, 36B is desired to be reduced ( Figure 3), to define a contact region that limits out-of-plane displacement (bumps) and to increase the out-of-plane capacitance in the Z detection region. Similarly and in a manner not shown, the groove 61 can be formed in other desired regions of the device, as discussed in detail below.

[0042] In Figure 8 , using a mask layer (second anchor mask) not shown, the second sacrificial layer 60 is further etched and selectively removed for its entire thickness, thereby forming an anchor opening 62. The etching of the second sacrificial layer 60 results in the formation of a hard mask region 60' and automatically terminates on the first epitaxial layer 41.

[0043] Generally, the second anchor opening 62 is formed where a connection region is needed between the first epitaxial layer 41 and the second epitaxial layer 42. Specifically, here, the second anchor opening 62 is formed where the second epitaxial layer 42 is anchored to the first epitaxial layer 41, where wide trenches and alignment structures in the first epitaxial layer 41 and the second epitaxial layer 42 are needed. In addition, the purpose of the hard mask region 60' is to allow defining a structure formed only in the first epitaxial layer 41 and bounded by wide trenches, as discussed below.

[0044] Specifically, due to the groove 61, the hard mask region 60' has two different thicknesses: a larger thickness equal to the thickness of the second sacrificial layer 60 and a smaller thickness at the groove 61.

[0045] Subsequently, Figure 9 , the second epitaxial layer 42 is grown, where the thickness of the second epitaxial layer 42 again depends on the desired microelectromechanical structure, and the thickness of the second epitaxial layer 42 can again be included between 2 and 80 μm. Generally, the second epitaxial layer 42 can be thinner than the first epitaxial layer 41, although the opposite may occur, and the present disclosure is not limited to any specific ratio between the thicknesses of the epitaxial layers 41, 42.

[0046] After epitaxial growth, the second epitaxial layer 42 is planarized and, for example, by CMP (chemical mechanical polishing) to reach the desired final thickness. In this way, the structural layer (also referred to as the monolithic epitaxial layer 64) formed by the first epitaxial layer 41 and the second epitaxial layer 42 reaches the final thickness, generally included between 20 and 80 μm.

[0047] In Figure 10 , an electrical connection region 65 (one in the drawing) is formed on the upper surface of the monolithic epitaxial layer 64 by depositing and patterning a metal layer such as aluminum or gold to define a contact pad.

[0048] In Figure 11In this case, the wafer 50 is etched. To this end, the wafer 50 is covered with a resist mask (second trench mask 66) and dry-etched. In this step, portions of the epitaxial layers 41 and 42 that are not covered by the second trench mask 66 and not covered by the hard mask region 60' are removed for the entire thickness of the overall epitaxial layer 64; in these regions, the etching is stopped on the first sacrificial layer 53. In contrast, regions that are not covered by the second trench mask 66 but are covered by the hard mask region 60' are removed only for the thickness of the second epitaxial layer 42.

[0049] Specifically, in this step, a second trench 67 that extends between the upper electrodes 36A, 36B and defines the upper electrodes 36A, 36B and has a depth equal to the thickness of the second epitaxial layer 42; a third trench 68 that extends for the entire thickness of the overall epitaxial layer 64 and defines a high-level structure (here, for example, a carrier pillar region 70 that supports an electrical connection region 65 and a fixed portion 45); and a cavity 69 that extends through the second epitaxial layer 42 and is defined at the bottom by the hard mask region 60' to form a structure (here, for example, in the lower region 71 of the second micro-machined structure 40) having a height equal to the thickness of the first epitaxial layer 41.

[0050] In some regions, the second trench 67, the third trench 68, and the cavity 69 may be wider than the first trench 58.

[0051] Subsequently, Figure 12 , the second trench mask 66 is removed; then the hard mask region 60', the portion of the second sacrificial layer 60 within the first trench 58, and the exposed portion of the first sacrificial layer 53 are removed, thereby releasing the micro-machined structures 35, 40, and the Z-stopper structure 38, and forming a first gap region 77 between the upper electrodes 36A, 36B and the lower electrodes 37A, 37B and a second gap region 78 below the lower electrodes 37A, 37B, as well as other suspended structures (also including the electrodes of the second micro-machined structure 40).

[0052] Accordingly, the remaining portions of the dielectric layer 51 and the first sacrificial layer 53 form the insulating layer 32.

[0053] Finally, the cover wafer is bonded to the wafer 50 via the bonding layer 46, and the overall wafer is diced to form Figure 3 the MEMS device 30. Alternatively, the wafer 50 is diced, and on the die thus obtained, the cover 44 is bonded in a known manner to obtain Figure 3 the structure.

[0054] In this way and with reference again to Figure 3, the first micromechanical structure 35 has: bottom electrodes 37A, 37B having a first thickness which is equal to the first epitaxial layer 41; upper electrodes 36A, 36B having a second thickness, where the second thickness is less than the first thickness and is approximately equal to the second epitaxial layer 42 in the first approximation; and a fixed central or anchoring portion 72 having a third thickness which is approximately equal to the sum of the first epitaxial layer 41 and the second epitaxial layer 42 (neglecting the thickness of the hard mask region 60' which is negligible with respect to the thicknesses of the first epitaxial layer 41 and the second epitaxial layer 42, and neglecting the thickness non-uniformity of the second epitaxial layer 42). In addition, the upper electrodes 36A, 36B have a thinner portion 73 (where the hard mask region 60' has a greater thickness, equal to the thickness of the second sacrificial layer 60) and a thicker portion 74, where the hard mask region 60' is thinner.

[0055] In addition, the thickness of the fixed portion 45 (which forms a peripheral wall around the micromechanical structures 35, 40 here and is thus referred to as the wall 45 hereinafter) and the carrier pillar region 70 is equal to the sum of the first epitaxial layer 41 and the second epitaxial layer 42.

[0056] In Figure 3 the MEMS device 30, the wall 45 also forms a protruding arm 75 which extends horizontally within the MEMS device 30 and covers an adjacent pillar 76 anchored to the substrate 31 at a certain distance.

[0057] The protruding arm 75 and the adjacent pillar 76 form a first Z-stopper structure 38, and the protruding arm 75 and the adjacent pillar 76 are respectively formed by the second epitaxial layer 42 and the first epitaxial layer 41 which are spaced apart from each other by a space equal to the thickness of the second sacrificial layer 60 ( Figure 7 ), having a complete thickness in this region, for example 1.6 μm. Alternatively, if a cavity 61 is also formed in this region, the distance between the protruding arm 75 and the adjacent pillar 76 can be equal to the distance between the upper electrode 36 and the bottom electrode 37 and equal to the thickness of the hard mask region 60'.

[0058] In addition, although in Figures 3 to 12 the adjacent pillar 76 is completely surrounded by trenches (a part of the first trench 58 and a part of the third trench 68), this is not necessary, and the adjacent pillar 76 can be replaced by a bottom adjacent region 76' which is only partially surrounded by, for example, the first trench 58, as Figure 13A shown.

[0059] According to another alternative, as Figure 13B shown, the adjacent pillar 76 can be formed by an unanchored portion 76'' supported by the first micromechanical structure 35.

[0060] The protruding arm 75 forms the upper adjacent area obtainable through the cantilever beam, but it can be formed by an adjacent wall of any shape.

[0061] In this way, the degree of Z movement of the micro - mechanical structures 35, 40 restricted to the substrate 31 can be set to be less than 2 μm and can be precisely controlled (with an accuracy of 10%) by the thickness of the mask area 60′, allowing for improved performance in the case of a vertical impact or drop of the MEMS device 30.

[0062] Furthermore, the possibility of forming electrodes (upper electrodes 36A, 36B and lower electrodes 37A, 37B) in two epitaxial layers 41, 42 that grow overlapping each other provides improved performance. In fact, when the MEMS device 30 is completed, the epitaxial layers 41, 42 are monolithic with each other and have the same mechanical and electrical properties. Thus, they act in the same way on external stresses (for example, in the case where the substrate 31 bends), because in this case, they will deform in the same way and degrade over time. Forming the upper electrodes 36A, 36B and the lower electrodes 37A, 37B with a central anchor makes them insensitive to stresses from substrate deformation, which is caused by, for example, heat treatment or mechanical strain induced on the substrate during soldering or during operation in the manufacturing steps.

[0063] Figures 14 to 16 The manufacturing steps according to an alternative process are shown.

[0064] Specifically, Figure 14 The wafer 50 after the Figure 9 step is shown and thus already includes the first epitaxial layer 41 and the second epitaxial layer 42, with a hard mask area (here called the first hard mask area 60′) embedded between them; there is also a first trench 58 that is partially filled with a portion of the second sacrificial layer 60.

[0065] In Figure 14 an electrical connection area 65 (one in this figure) is formed on the second epitaxial layer 42, and the wafer 50 is etched to define the upper electrodes 36A, 36B. For this purpose, the wafer 50 is covered by a different second trench mask, indicated by 81 herein, and the wafer 50 is dry - etched to remove only the exposed portion of the second epitaxial layer 42. The etching stops completely on the first hard mask area 60′ here and results in the formation of a second trench 67 that extends between the upper electrodes 36A, 36B.

[0066] Then, Figure 15, the second trench mask 81 is removed, an electrical connection region 65 (one in this figure) is formed on the upper surface of the overall epitaxial layer 64, and a second hard mask region 82 is formed on the surface of the wafer 50 to protect the second trench 67. For example, the second hard mask region 82 is formed by depositing and defining another sacrificial layer such as TEOS (which can fill a part of the second trench 67 here). In this way, the resist, which is more difficult to remove subsequently, is prevented from entering the second trench 67.

[0067] Subsequently, a third trench mask 85, such as a resist, is formed and covers the surface of the wafer 50, which surface includes the second hard mask region 82 and the electrical connection region 65, and exposes the surface of the overall epitaxial layer 64 where it is desired to form a third trench 68 extending through the entire overall epitaxial layer 64 or where it is desired to form a cavity 69 extending only through the second epitaxial layer 42 above a lower structure protected by the first hard mask region 60'.

[0068] Then, Figure 16 , the second epitaxial layer 42 and the first epitaxial layer 41 are selectively removed to form the third trench 68 and the cavity 69.

[0069] Then, the third trench mask 85, the second hard mask region 82 (including the part within the second trench 67), the first hard mask region 60' (including the part within the first trench 58), and the exposed part of the first sacrificial layer 53 are removed to release the micro - mechanical structures 35, 40 and form a first gap region 77 and a second gap region 78.

[0070] Then, followed are the final steps of the MEMS device 30 that have been described with reference to Figure 12 and result in Figure 3 .

[0071] Using Figures 14 to 16 's solution, high dimensional accuracy can be obtained because the sizes of the openings in the second trench mask 81 (intended to define the second narrower trench 67) and the third trench mask 85 (intended to define the third wider trench 68 and the cavity 69) can be better controlled with reference to the specific widths of the trenches and the regions to be removed.

[0072] The MEMS devices and manufacturing processes described herein have many advantages.

[0073] Specifically, they allow multiple micro - mechanical structures of various types to be arranged in a single die, allowing the overall size to be reduced, reducing the manufacturing cost, and improving the integration of portable devices, where the device footprint is important both in terms of space and cost.

[0074] The size of each region and especially the thickness can be chosen very freely based on the desired structure and with high dimensional control. For example, a structure with high quality in the lower epitaxial layer (such as a gyroscope) and a thinner structure in the upper epitaxial layer (such as an accelerometer) can be formed; or the entire thickness of the overall epitaxial layer 64 can be used to form a single structure with a very high thickness. Generally, due to the high thickness available, a high sensitivity related to the quality of the sensitive region can be obtained.

[0075] In addition, as explained, structures with at least three different base heights can be formed, which can be modulated as explained above for the upper electrodes 36A, 36B.

[0076] This process is particularly reliable because it is based on well-known individual process steps and has no critical intermediate steps or structures. Therefore, the MEMS device has high reliability.

[0077] Two or more different structures that are monolithic with each other can be stacked, resulting in very high behavioral uniformity and stability with respect to manufacturing defects and diffusion, interference and external actions, stress and changes over time.

[0078] This process allows for the formation of optimized stop structures that are less sensitive to external influences compared to known solutions, such as for example the Z - stopper structure 38, where two adjacent parts are anchored to the substrate and thus undergo equal stress and deformation, making the MEMS device more durable and reliable.

[0079] Finally, it is obvious that modifications and variations can be made to the manufacturing processes and MEMS devices described and illustrated herein without thereby departing from the scope of protection of the present disclosure, as defined in the appended claims.

[0080] For example, if needed, a third level can be formed to grow a third epitaxial layer and thus increase the available height levels and / or the number of integrable structures.

[0081] In addition, although the structures shown are capacitive sensors, this process can also be used to form drive structures, also utilizing different physical principles, such as systems based on electrostatic actuation.

[0082] As discussed above, the Z - stop structure 38 can be the bottom adjacent region 76 in the first epitaxial layer 41 and the differently shaped upper adjacent region 75 in the second epitaxial layer 42.

[0083] In some embodiments, a process for fabricating a MEMS device (30) may be outlined to include: forming a first structural layer (41) of semiconductor material on a substrate (31), the first structural layer having a first thickness; forming a plurality of first trenches (58) that extend through the first structural layer (41) and define first functional elements (37A, 37B); forming mask regions (60') on the first structural layer, the mask regions being separated from each other by first openings (62); forming a second structural layer (42) of semiconductor material on the first structural layer (41) and the mask regions (60'), the second structural layer having a second thickness, the second structure being in direct contact with the first structural layer (41) at the first openings (62) and together with the first structural layer forming a thick structural region (64) of semiconductor material having a third thickness, the third thickness being equal to the sum of the first thickness and the second thickness; forming a plurality of second trenches (67) that extend through the second structural layer (42) above the mask regions (60'); and forming a plurality of third trenches (68) that extend through the first and second structural layers (41, 42) by removing a selective portion of the thick structural region (64).

[0084] In some embodiments, the second trenches (67) define first functional regions (36A, 36B) having a second thickness; the third trenches (68) define second functional regions (45, 70) having a third thickness; the process further includes removing a selective portion of the second structural layer (42) to form a cavity (69) above the mask regions (60') when forming the third trenches (68), thereby forming a third region (71) having a first thickness.

[0085] In some embodiments, forming the second trenches (67) and forming the third trenches (68) includes using a single etch mask (66).

[0086] In some embodiments, forming the second trenches (67) and forming the third trenches (68) includes using two different etch masks (81, 85).

[0087] In some embodiments, the third trenches (68) have a width greater than that of the second trenches (67).

[0088] In some embodiments, forming the mask regions (60') includes forming a mask sacrificial layer (60) and patterning the mask sacrificial layer.

[0089] In some embodiments, further includes removing the mask regions (60') and forming a first gap region (77) between the first structural layer and the second structural layer (41, 42).

[0090] In some embodiments, the method includes: forming a sacrificial anchor layer (53) over a substrate (31) before forming a first structural layer (41), the sacrificial anchor layer having an anchor opening (55), and removing a mask region (60') includes removing the sacrificial anchor layer (53) and forming a second gap region (78) between the first structural layer (41) and the substrate (31).

[0091] In some embodiments, the method includes forming a vertical stop structure (38), including forming a bottom adjacent region (76) in the first structural layer (41) and an upper adjacent region (75) in the second structural layer (42), the bottom adjacent region (76) having a first thickness and being at least partially defined by a first trench (58) belonging to a plurality of first trenches and / or by a lower portion of an adjacent trench (68) belonging to a plurality of third trenches (68), and the upper adjacent region (75) being superimposed on the bottom adjacent region (76), and the upper adjacent region (75) being separated from the bottom adjacent region by a first gap region (77) among a plurality of first gap regions.

[0092] In some embodiments, the upper adjacent region (75) is defined by a second trench (68) belonging to a plurality of second trenches and / or by an upper portion of the adjacent trench (68).

[0093] In some embodiments, forming a plurality of first trenches (58) includes defining first functional elements (37A, 37B), and forming a plurality of second trenches (67) includes defining second functional elements (36A, 36B).

[0094] In some embodiments, a MEMS device (30) can be generally described as including: a substrate (31); a first structural layer (41), having a first thickness and extending over the substrate; a second structural layer (42), having a second thickness and extending over the first structural layer; a plurality of first trenches (58), extending through the first structural layer (41) and defining first functional elements (37A, 37B); a plurality of second trenches (67), extending through the second structural layer (42) and defining second functional elements (36A, 36B) superimposed on the first functional elements; and a plurality of third trenches (68), extending through the first structural layer and the second structural layer (41, 42), wherein the first structural layer and the second structural layer form a support structure (72), having a third thickness equal to the sum of the first thickness and the second thickness, the support structure being anchored to the substrate (31) and supporting the first functional elements and the second functional elements (37A, 37B, 36A, 36B), and wherein a first gap region (77) extends between the first functional elements and surrounds the support structure (72).

[0095] In some embodiments, the MEMS device further includes: a vertical stop structure (38) including a bottom adjacent region (76) and an upper adjacent region (75) stacked on top of each other, the bottom adjacent region (76) extending in a first structural layer (41), having a first thickness and at least partially defined by a first trench (58) belonging to a plurality of first trenches and / or by a lower portion of an adjacent trench (68) belonging to a plurality of third trenches, and the upper adjacent region (75) extending in a second structural layer (42), having a second thickness and separated from the bottom adjacent region (75) by an adjacent gap region (77).

[0096] In some embodiments, the upper adjacent region (75) is defined by a second trench (68) belonging to a plurality of second trenches and / or by an upper portion of the adjacent trench (68).

[0097] In some embodiments, the MEMS device further includes: a first functional region (75) having a second thickness and defined by a second trench or a third trench (67, 68); a second functional region (70) having a third thickness and defined by a third trench (68); and a third functional region (71) having a first thickness and defined by a first trench (58) and / or a lower portion of a third trench (68).

[0098] The various embodiments described above can be combined to provide other embodiments. In view of the description detailed above, these and other changes can be made to the embodiments. Generally, in the following claims, the terms used should not be construed as limiting the claims to the specific embodiments disclosed in this specification and the claims, but should be construed to include all possible embodiments and the entire scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the present disclosure.

Claims

1. A process for manufacturing a MEMS device, comprising: forming a first structural layer of semiconductor material on a substrate, the first structural layer having a first thickness; forming a plurality of first trenches extending through the first structural layer and defining a first functional element; forming mask regions on the first structural layer, the mask regions being separated from each other by first openings; forming a second structural layer of semiconductor material on the first structural layer and the mask regions, the second structural layer having a second thickness, the second structural layer being in direct contact with the first structural layer at the first openings, and the second structural layer and the first structural layer together forming a thick structural region of the semiconductor material having a third thickness, the third thickness being equal to the sum of the first thickness and the second thickness; forming a plurality of second trenches extending through the second structural layer above the mask regions; and forming a plurality of third trenches extending through the first structural layer and the second structural layer by removing a selective portion of the thick structural region; wherein the process further comprises: forming a plurality of first gap regions between the first structural layer and the second structural layer; and forming a vertical stop structure, comprising forming a bottom adjacent region in the first structural layer and an upper adjacent region in the second structural layer, the bottom adjacent region having the first thickness and being at least partially defined by a first trench belonging to the plurality of first trenches or by a lower portion of an adjacent trench belonging to the plurality of third trenches, and the upper adjacent region covering the bottom adjacent region and being separated from the bottom adjacent region by a first gap region among the plurality of first gap regions.

2. The process according to claim 1, wherein the second trenches define a first functional region having the second thickness, and the third trenches define a second functional region having the third thickness, and the process further comprises: removing a selective portion of the second structural layer to form a cavity above the mask regions when forming the third trenches, thereby forming a third region having the first thickness.

3. The process according to claim 1, wherein forming the second trench and forming the third trench comprise: using a single etch mask to form the second trenches and the third trenches.

4. The process according to claim 1, wherein forming the second trench and forming the third trench comprise: using two different etch masks to form the second trenches and the third trenches.

5. The process according to claim 1, wherein the third trenches have a width greater than that of the second trenches.

6. The process according to claim 1, wherein forming the mask region comprises: forming a mask sacrificial layer and patterning the mask sacrificial layer.

7. The process according to claim 1 further comprises: removing the mask regions.

8. The process according to claim 7, comprising: forming a sacrificial anchor layer having an anchor opening above the substrate before forming the first structural layer; and removing the mask regions, removing the mask regions comprising: removing the sacrificial anchor layer and forming a second gap region between the first structural layer and the substrate.

9. The process according to claim 1, wherein the upper adjacent region is defined by a second trench belonging to the plurality of second trenches or by an upper portion of the adjacent trench.

10. The process according to claim 1, wherein forming a plurality of first trenches comprises: defining a first functional element, and forming a plurality of second trenches comprising: defining a second functional element.

11. A MEMS device, comprising: a substrate; a first structural layer having a first thickness and extending over the substrate; a second structural layer having a second thickness and extending over the first structural layer; a plurality of first trenches extending through the first structural layer and defining a first functional element; a plurality of second trenches extending through the second structural layer and defining a second functional element covering the first functional element; and a plurality of third trenches extending through the first structural layer and the second structural layer, wherein the first structural layer and the second structural layer form a support structure having a third thickness equal to the sum of the first thickness and the second thickness, the support structure being anchored to the substrate and supporting the first functional element and the second functional element, and wherein a first gap region extends between the first functional element and the second functional element and surrounds the support structure.

12. The MEMS device according to claim 11, further comprising: a vertical stop structure including a bottom abutment region and an upper abutment region covering the bottom abutment region, wherein the bottom abutment region extends in the first structural layer, has the first thickness, and is at least partially defined by a first trench belonging to the plurality of first trenches or by a lower portion of an adjacent trench belonging to the plurality of third trenches, and wherein the upper abutment region extends in the second structural layer, has the second thickness, and is separated from the bottom abutment region by an adjacent gap region.

13. The MEMS device according to claim 12, wherein the upper abutment region is defined by a second trench belonging to the plurality of second trenches or by an upper portion of the adjacent trench.

14. The MEMS device according to claim 11, further comprising: a first functional region having the second thickness and defined by the second trench or the third trench; a second functional region having the third thickness and defined by the third trench; and a third functional region having the first thickness and defined by the first trench or a lower portion of the third trench.

15. The MEMS device according to claim 11, wherein the width of the second functional element is greater than the width of the first functional element.

16. A method, comprising: forming a plurality of first trenches extending through a first semiconductor layer and defining a first functional element, the first semiconductor layer having a first thickness; forming mask regions on the first semiconductor layer, the mask regions being separated from each other by openings; forming a second semiconductor layer on the first semiconductor layer and the mask regions, the second semiconductor layer directly contacting the first semiconductor layer at the openings; forming a plurality of second trenches extending through the second semiconductor layer and at least partially exposing portions of the mask regions; forming a cavity and a plurality of third trenches by selectively removing portions of the second semiconductor layer, the cavity covering at least one of the mask regions in the mask regions, the plurality of third trenches extending from the cavity through the second semiconductor layer; The method further includes: Forming a plurality of first gaps between the first semiconductor layer and the second semiconductor layer by removing the mask regions; And Forming a vertical stop structure, including forming a bottom adjacent region in the first semiconductor layer and an upper adjacent region in the second semiconductor layer, the bottom adjacent region having the first thickness and being at least partially defined by a first trench belonging to the plurality of first trenches or by a lower portion of an adjacent trench belonging to the plurality of third trenches, and the upper adjacent region covering the bottom adjacent region and being separated from the bottom adjacent region by a first gap among the plurality of first gaps.

17. The method according to claim 16, wherein forming the second trench and forming the third trench comprise: Using a single etching mask to form the second trench and the third trench.

18. The method according to claim 16, wherein forming the second trench and forming the third trench comprise: Using two different etching masks to form the second trench and the third trench.

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