Process for manufacturing microelectromechanical device with reduced static friction phenomena

Abstract

The invention relates to a process for manufacturing a micro-electro-mechanical device with reduced static friction phenomena. A manufacturing process of a micro-electro-mechanical device includes: forming a sacrificial layer of a dielectric material on a body including a semiconductor material, the sacrificial layer having a first surface opposite the body; imparting a sacrificial surface roughness to the first surface of the sacrificial layer; on the first surface of the sacrificial layer, a structural layer of semiconductor material having a second surface is formed, the second surface being in contact with the first surface of the sacrificial layer. Imparting a sacrificial surface roughness to a first surface of a sacrificial layer includes: forming a transfer layer of a semiconductor material having an intrinsic porosity on the sacrificial layer; and partially removing the sacrificial layer through the transfer layer.

Description

Technical Field

[0001] The present disclosure relates to processes for fabricating microelectromechanical (MEMS) devices having reduced stiction. Background Art

[0002] The operation of inertial microelectromechanical (MEMS) devices (in particular, such as gyroscopes and accelerometers) is based on a mass coupled to a support (such as, for example, a frame or substrate of semiconductor material), the mass freely oscillating in one or more directions relative to the support in order to sense changes in physical quantities or act as an actuator. These masses are collectively referred to as "movable" or "suspended" masses and are also formed of semiconductor materials, typically, for example, polycrystalline silicon or single crystal silicon.

[0003] During operation of a MEMS device or in response to an impact, one or more movable masses may oscillate to the point of mechanical interference with each other or with a static element of the device (e.g., a stopper or common support). Contact between surfaces of semiconductor materials may cause an adhesion phenomenon known as "stiction", especially if formed from the same semiconductor material (such as, for example, silicon). Stiction may be irreversible, for example causing the movable mass to adhere to the static element, and may impair the function of the entire device.

[0004] Stiction can be caused by both "in-plane" and "out-of-plane" oscillations of the movable mass. Generally, stiction due to out-of-plane oscillations is the most critical due to the size of the surfaces involved. Summary of the invention

[0005] The present disclosure provides methods for overcoming or at least partially alleviating the disadvantages and limitations of the prior art.

[0006] According to the present disclosure, a manufacturing process of a micro-electromechanical device is provided. The manufacturing process of the micro-electromechanical device includes forming a sacrificial layer of a dielectric material on a body including a semiconductor material, the sacrificial layer having a first surface opposite to the body. A sacrificial surface roughness is generated on the first surface of the sacrificial layer by forming a transfer layer of a semiconductor material having an inherent porosity on the sacrificial layer and partially removing the sacrificial layer through the transfer layer. On the first surface of the sacrificial layer, a structural layer of a semiconductor material is formed, the structural layer having a second surface in contact with the first surface of the sacrificial layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] For a better understanding of the present disclosure, preferred embodiments are now provided by way of non-limiting examples with reference to the accompanying drawings, in which:

[0008] Figure 1a to Figure 1bschematically shows in cross section a portion of a MEMS device according to the prior art in two corresponding conditions;

[0009] Figure 2 A portion of a MEMS device according to an embodiment of the present disclosure is schematically shown in cross section;

[0010] Figure 3 A portion of a MEMS device according to various embodiments of the present disclosure is schematically shown in cross section;

[0011] Figure 4a to Figure 4g The following schematically illustrates in cross section the process of sequential processing steps in a manufacturing process according to an embodiment of the present disclosure. Figure 2 MEMS devices; and

[0012] Figure 5a to Figure 5g The following schematically illustrates in cross section the process of sequential processing steps in a manufacturing process according to various embodiments of the present disclosure. Figure 3 MEMS devices. DETAILED DESCRIPTION

[0013] Figure 1a A part of a generic MEMS device 1 (e.g. an inertial sensor) is shown, comprising a movable mass 2, which is suspended relative to a multilayer 3 by means of an anchor 4. The movable mass 2 can oscillate relative to the multilayer 3 along a direction of movement D (here, for example, in an out-of-plane oscillation). The multilayer 3 comprises a polysilicon layer, in which, for example, fixed electrodes and / or buried electrical connections are formed. The MEMS device 1 can suffer from stiction phenomena between the movable mass 2 and the multilayer 3, in particular between corresponding facing silicon surfaces, in particular if these surfaces have a substantially flat profile. As Figure 1b As shown in , the movable mass 2 may be attached to the underlying surface in an irreversible manner.

[0014] The most widespread solution to limit the stiction problem may consist in reducing the contact area between the movable mass 2 and the multilayer 3, and / or treating the facing surfaces of the movable mass 2 and the multilayer 3 (such as, for example, applying an anti-stiction coating). However, such solutions may impose severe restrictions on the design of the elements of the MEMS device, for example, on the size and material of the movable mass, which may result in reduced performance, or they may include complex additional steps in the manufacturing process that complicate their implementation.

[0015] Figure 2A portion of a microelectromechanical or MEMS device 10 (e.g., an inertial sensor, such as an accelerometer or a gyroscope) according to one embodiment of the present disclosure is illustrated. The MEMS device 10 includes a movable mass 12 and a multilayer 13, the movable mass 12 being coupled relative to the multilayer 13 so as to be able to oscillate along a direction of motion D. In detail, the movable mass 12 is suspended relative to the multilayer 13 by a fixed anchor 14, and the oscillations of the movable mass 12 along the direction of motion D are "out-of-plane": considering a reference system of axes X, Y, Z that are transverse to each other, the movable mass 12 and the multilayer 13 actually extend mainly in a plane parallel to the XY plane, and the direction of motion D (e.g., the sensing or driving direction) is parallel to the Z axis. Therefore, the MEMS device 10 is able to sense or actuate displacements along the Z axis, and in Figure 2 1 is shown in a rest condition, i.e. when the movable mass 12 is at rest. By way of non-limiting example, the movable mass 12 may be a membrane, a cantilever structure or a structure oscillating about a fulcrum axis perpendicular to the Z axis (a "seesaw"). In the latter case, the movable mass 12 may be coupled to the anchor by a flexure not shown for simplicity.

[0016] The movable mass 12 of the MEMS device 10 is polycrystalline silicon and may include a plurality of elements, not shown, such as electrodes, that are movable relative to the multilayer 13. The multilayer 13 is a structure of different layers stacked and in contact with each other and includes a substrate 15 of a semiconductor material (e.g., of single crystal silicon), a permanent dielectric layer 16, such as silicon oxide, arranged on the substrate 15, and a connection layer 17, such as polycrystalline silicon, arranged on the permanent dielectric layer 16. The connection layer 17 is appropriately doped so as to be conductive and is patterned so as to form, for example, fixed electrodes (not shown in detail) that are capacitively coupled to the plurality of movable electrodes of the movable mass 12. Alternatively, the fixed electrodes may again be directly coupled to the movable mass 12 in a capacitive manner. An anchor 14, also, for example, polycrystalline silicon, is fixed to the multilayer 13 and more particularly to the connection layer 17.

[0017] The movable mass 12 and the connecting layer 17 are provided with respective main faces 12a, 17a facing each other, the main faces 12a, 17a being parallel to each other in a first approximation and extending perpendicularly to the Z axis. The main faces 12a of the movable mass 12 and the main faces 17a of the connecting layer 17 are separated from each other along the Z axis by a distance at least equal to the size of the anchor 14.

[0018] like Figure 2As shown in , the main surface 17a of the connection layer 17 has an intentionally caused roughness, which is referred to as the connection surface roughness hereinafter. According to one aspect of the present disclosure and as described in more detail below, the main surface 12a of the movable mass block 12 also has an intentionally caused roughness, which is referred to as the structural surface roughness. The connection surface roughness and the structural surface roughness can be different from each other. The connection surface roughness and the structural surface roughness have the effect of reducing the static friction phenomenon between the movable mass 12 and the multilayer 13, and generally have the effect of increasing the static friction against the MEMS device 10.

[0019] Figure 3 A portion of a MEMS device 20 according to various embodiments is illustrated. Elements already present in the MEMS device 10 are indicated with the same reference numerals; moreover, as will become clearer below, the MEMS device 20 is manufactured using different steps relative to the steps used to manufacture the MEMS device 10 .

[0020] The MEMS device 20 includes a support substrate 25 of semiconductor material, in particular, single crystal silicon, a dielectric bonding layer 26, such as silicon oxide, arranged on the support substrate 25, and a connection layer 27, such as polysilicon, arranged on the dielectric bonding layer 26. The MEMS device 20 also includes a movable mass 22, which is coupled to the connection layer 27 by the anchor 14 and is suspended relative to the connection layer 27 so as to be able to oscillate along the direction of motion D.

[0021] The movable mass 22 extends mainly in a plane parallel to the xy plane, is formed of single crystal silicon, and comprises a plurality of elements, not shown, movable relative to the connection layer 27, such as electrodes. The connection layer 27 is appropriately doped so as to be conductive and is patterned so as to form fixed electrodes (not shown in detail) that are capacitively coupled to the plurality of movable electrodes of the movable mass 22, for example. Alternatively, the fixed electrodes may be directly coupled to the movable mass 22, again in a capacitive manner. The MEMS device 20 is Figure 3 2 is shown in a parked condition, ie when the movable mass 22 is stationary.

[0022] The movable mass 22 and the connecting layer 27 are provided with respective main faces 22a, 27a facing each other, the main faces 22a, 27 extending parallel to each other in a first approximation and perpendicular to the Z axis. The main faces 22a of the movable mass 22 and the main faces 27a of the connecting layer 27 are separated from each other along the Z axis by a distance at least equal to the size of the anchor 14.

[0023] In the MEMS device 20, as Figure 3As can be seen in FIG. 1 , the main surface 27a of the connection layer 27 has a roughness that is intentionally caused and corresponds to the structural surface roughness mentioned above. The structural surface roughness has the function of reducing the static friction phenomenon between the movable mass 22 and the connection layer 27, and has the function of increasing the static friction against the MEMS device 20 as a whole.

[0024] Figure 2 The MEMS device 10 is obtained by an embodiment of the manufacturing process subject of the present disclosure, the successive steps of which are as follows: Figure 4a to Figure 4g Shown in.

[0025] Figure 4a A semiconductor wafer including a substrate 15 is shown in cross section. A permanent dielectric layer 16 is formed over and in contact with the substrate 15, for example by chemical vapor deposition (CVD) of silicon oxide or by thermal oxidation. Then, a first polysilicon layer 117 is formed over and in contact with the permanent dielectric layer 16, for example by deposition and more particularly by CVD. The first polysilicon layer 117 has an exposed surface that substantially corresponds to the main face 17a of the connection layer 17. The first polysilicon layer 117 is doped with, for example, phosphorus or boron and has a thickness along the Z axis, for example, between 100 nm and 5 μm.

[0026] The first polysilicon layer 117 is formed so as to be arranged on the corresponding main surface 17a ( Figure 4b ) is formed with a predetermined roughness corresponding to the connection surface roughness. For example, for the connection surface roughness, a roughness root mean square (RMS) value between 5 nm and 50 nm (including the end value) (a typical value is, for example, equal to 20 nm) and a peak-to-peak value between 120 nm and 230 nm (a typical value is, for example, equal to 210 nm) measured along the Z axis can be obtained.

[0027] therefore, Figure 2 The connection layer 17 is formed by the first polysilicon layer 117: Although not shown in the drawings, it should be understood that the present manufacturing process includes a step of patterning conductive areas (such as, for example, fixed electrodes and connections buried in the permanent dielectric layer 16) within the first polysilicon layer 117.

[0028] The sacrificial layer 18 is formed on the connection layer 17 ( Figure 4c ) and its thickness is at least equal to the dimension of the anchor 14 of the MEMS device 10 along the Z axis. The sacrificial layer 18 is formed of a dielectric, such as silicon oxide. The sacrificial layer 18 thus formed has an exposed surface hereinafter referred to as a transfer surface 18a.

[0029] refer to Figure 4dThe transfer layer 19 is formed, for example, by deposition, above the sacrificial layer 18 and in particular in contact with the transfer surface 18a, and has a thickness, for example, between 50 nm and 250 nm (typical values, for example, equal to 100 nm); therefore, the transfer layer 19 is considered "thin" relative to the sacrificial layer 18. The transfer layer 19 is formed of a semiconductor material having an intrinsic porosity. The transfer layer 19 is, for example, polycrystalline silicon having an intrinsic porosity of a full / empty mass ratio lower than 80%.

[0030] Applicants have demonstrated that by performing a dry etch through the transfer layer 19 ( Figure 4e ), the sacrificial layer 18 is partially removed, and a predetermined roughness ( Figure 4f ), which is called the sacrificial surface roughness. This roughness of the transfer surface 18a is determined by the fact that the removal of the sacrificial layer 18 is irregular due to the intrinsic porosity of the transfer layer 19. The dry removal can be, for example, anisotropic plasma ion bombardment of the transfer layer 19 performed using fluorine and / or bromine and / or chloride ions and a pressure between 6 mTorr and 70 mTorr in the etching chamber.

[0031] The sacrificial layer 18 is then patterned by known photolithography techniques to obtain corresponding openings (not shown) in which supporting structures (such as, for example, anchors 14 ) of the movable mass 12 of the MEMS device 10 are later formed.

[0032] refer to Figure 4g , a second polysilicon layer 112 is formed, for example by deposition, over the sacrificial layer 18 and in particular in contact with the transfer surface 18a, having a thickness along the Z axis, for example, between 1 μm and 100 μm. The surface of the second polysilicon layer 112 in contact with the transfer surface 18a is denoted by the transferred surface 112a. In this step, the opening in the sacrificial layer 18 is filled and a support structure, in particular an anchor 14, for the movable mass 12 of the MEMS device 10 is formed.

[0033] According to one aspect of the present disclosure, since the second polysilicon layer 112 is formed in contact with the sacrificial layer 18, the transferred surface 112a of the second polysilicon layer 112 obtains a roughness characteristic that is complementary to the roughness of the transfer surface 18a of the sacrificial layer 18 in a first approximation. In practice, the second polysilicon layer 112 and, in more detail, the corresponding transferred surface 112a are obtained by using the sacrificial layer 18 as a mold. The roughness of the transferred surface 112a corresponds to the structural surface roughness of the MEMS device 10 and is complementary to the sacrificial surface roughness of the transfer surface 18a, thereby replicating its profile "in a complementary manner". The profile of the transferred surface 112a is actually obtained by transferring the profile of the sacrificial layer 18.

[0034] For example, for the surface roughness of the structure, a roughness root mean square (RMS) value between 5 nm and 20 nm (typical value, for example, equal to 8 nm) and a peak-to-peak value measured along the Z axis between 10 nm and 100 nm (including the end values) (typical value, for example, equal to 40 nm) can be obtained.

[0035] Finally, the second polysilicon layer 112 is patterned to form the movable mass 12 and structures associated therewith (such as, for example, flexures) of the MEMS device 10. In detail, the second polysilicon layer 112 is exposed, for example by dry removal, down to the sacrificial layer 18 to pattern the flexures and any other elements not shown according to design preferences. Wherever left, the transferred surface 112a thus forms the main surface 12a of the movable mass 12. The sacrificial layer 18 is then selectively removed, for example in a hydrofluoric acid environment, and the movable mass 12 is released, thereby achieving Figure 2 The MEMS device 10.

[0036] Figure 3 The MEMS device 20 is obtained by different embodiments of the manufacturing process subject of the present disclosure, the successive steps of which are as follows: Figure 5a to Figure 5g Elements that are already present in the manufacturing process of the MEMS device 10 are indicated with the same reference numerals.

[0037] Figure 5a A work wafer 122 of single crystal silicon is shown in cross section. A sacrificial layer 28 is formed, for example by deposition, over and in contact with the work wafer 122, with a thickness at least equal to the dimension of the anchor 14 of the MEMS device 20 along the Z axis. The sacrificial layer 28 is formed of a dielectric, for example of silicon oxide. The sacrificial layer 28 thus formed is provided with an exposed surface, hereinafter referred to as a transfer surface 28a.

[0038] Basically as already referenced Figure 4d and Figure 4eThe transfer layer 119 is described as being formed above the sacrificial layer 28 and in particular in contact with the transfer surface 28a ( Figure 5b ).

[0039] The dry removal of the sacrificial layer 28 is performed by passing through the transfer layer 119 as previously described ( Figure 5c ), giving the transfer surface 28a an intermediate surface roughness ( Figure 5d ).

[0040] The sacrificial layer 28 is then patterned by known photolithographic techniques to obtain corresponding openings (not shown), wherein the support structures of the movable mass 22 of the MEMS device 20 (such as, for example, the anchors 14 ) are then formed.

[0041] refer to Figure 5e The polysilicon layer corresponding to the connection layer 27 of the MEMS device 20 is formed, for example, by deposition or epitaxial growth, over the sacrificial layer 28 and in particular in contact with the transfer surface 28a, and has a thickness along the Z axis of, for example, between 100 nm and 5 μm. The connection layer 27 is doped with, for example, phosphorus or boron in order to give it the desired conductive properties. The surface of the connection layer 27 in contact with the transfer surface 28a of the sacrificial layer 28 corresponds to Figure 3 The main surface 27a of the embodiment of the present invention is shown in FIG. 2 and is interchangeably referred to as the transferred surface 27a.

[0042] According to one aspect of the present disclosure, since the connection layer 27 is formed in contact with the sacrificial layer 28, the transferred surface 27a of the connection layer 27 acquires a roughness characteristic that is complementary to the roughness of the transfer surface 28a of the sacrificial layer 28 in a first approximation. In practice, the connection layer 27 and, in more detail, the corresponding transferred surface 27a are obtained by using the sacrificial layer 28 as a mold. The roughness of the transferred surface 27a corresponds to the structural surface roughness of the MEMS device 20 and is complementary to the sacrificial surface roughness of the transfer surface 28a, thereby replicating its profile "in a complementary manner". The profile of the transferred surface 27a is actually obtained by transferring the profile of the sacrificial layer 28.

[0043] Finally, a forming step and a patterning step are then performed to form the movable mass 22 and structures related thereto (such as, for example, flexures) of the MEMS device 20. In detail, the movable mass 22 of the MEMS device 20 is obtained by semiconductor wafer bonding technology (referred to as wafer-wafer bonding technology).

[0044] refer to Figure 5fA silicon oxide layer is formed over and in contact with the connection layer 27, for example, by CVD deposition, thereby forming a dielectric bonding layer 26. A handle single crystal silicon wafer is bonded to the connection layer 27 through the dielectric bonding layer 26, for example, by a thermal bonding process. The handle single crystal silicon wafer includes a substrate intended to form a support substrate 25 of the MEMS device 20.

[0045] Then, Figure 5f The wafer is flipped relative to the Z axis ( Figure 5g ), thus obtaining Figure 3 , wherein the support substrate 25 is located below the connection layer 27. Then, the working wafer 122 of single crystal silicon is exposed up to the sacrificial layer 28, so as to pattern the movable mass 22, and, for example, by dry removal, the flexure and any other elements not shown are patterned according to design preferences. Finally, the sacrificial layer 28 is selectively removed, for example, by removal in a hydrofluoric acid environment, and the movable mass 22 is released, so as to achieve Figure 3 MEMS device 20.

[0046] The manufacturing process according to the two embodiments described above allows single-crystal silicon and polycrystalline silicon to be used alternatively for the movable mass block of the MEMS device. According to the above steps, the roughness intentionally caused on the surface of the movable mass block and on the surface of the structure below the movable mass block, and in particular on the surface of the conductive layer (of polycrystalline silicon) arranged facing the movable mass block, allows to reduce the phenomenon of static friction between the movable mass block and the structure below. In particular, the steps of forming these surface roughnesses are easy to implement; moreover, the transfer of roughness characteristics between different successively formed layers makes the process controllable and flexible in terms of the obtainable profile. In more detail, by the present manufacturing process, the choice of semiconductor material for the movable mass block is independent of the choice of semiconductor material for the structure below (such as, the conductive layer), for example, they can be different from each other. In addition, the formation of the surface roughness is independent of the steps of forming the corresponding structure, and in particular independent of the subsequent processing flow.

[0047] Finally, modifications and variations may be made to what is described and illustrated herein without departing from the scope of the present disclosure as defined in the appended claims.

[0048] For example, the movable mass may be a structure having a cantilever element (referred to as a "cantilever"), and the MEMS device may be an electroacoustic transducer. Alternatively, the movable mass may be a diaphragm capable of vibrating, for example, in a pressure sensor. Or in addition, the MEMS device may be an accelerometer configured for out-of-plane measurements, and the cross-section of the movable mass has the shape of a beam capable of oscillating about a non-center-of-gravity axis.

[0049] In a variant not shown, the connection surface roughness and / or the structure surface roughness is formed in a non-uniform and / or localized manner on the respective surface. For example, using a specific mask, the surface roughness can be locally selectable.

[0050] A manufacturing process of a micro-electromechanical device (10; 20) comprises: forming a sacrificial layer (18; 28) of a dielectric material having a first surface (18a; 28a) opposite to the body (13; 122) on a body (13; 122) comprising a semiconductor material; generating sacrificial surface roughness on the first surface (18a; 28a) of the sacrificial layer (18; 28) by forming a transfer layer (19; 119) of a semiconductor material having an intrinsic porosity on the sacrificial layer (18; 28) and partially removing the sacrificial layer (18; 28) through the transfer layer (19; 119); and forming a structural layer (112; 27) of a semiconductor material having a second surface (112a; 27a) in contact with the first surface (18a; 28a) of the sacrificial layer (18; 28) on the first surface (18a; 28a) of the sacrificial layer (18; 28).

[0051] The sacrificial surface roughness is defined by a root mean square value between 5 nm and 20 nm.

[0052] The transfer layer (19; 119) comprises polycrystalline silicon having an intrinsic porosity with a full / empty mass ratio lower than 80%.

[0053] The sacrificial layer (18; 28) comprises silicon oxide.

[0054] Partially removing the sacrificial layer (18; 28) includes dry etching the sacrificial layer (18; 28).

[0055] The body (13) comprises: a substrate (15) of semiconductor material; a permanent dielectric layer (16) arranged on the substrate (15); and a conductive connection layer (17) arranged on the permanent dielectric layer (16).

[0056] The manufacturing process also includes: anchoring the structural layer (112) to the connecting layer (17); forming a movable mass block (12) from the structural layer (112); and selectively removing the sacrificial layer (18) to thereby release the movable mass block (12), wherein the movable mass block (12) is constrained to the connecting layer (17) so as to be able to oscillate along a direction (D) transverse to the connecting layer (17).

[0057] The manufacturing process also includes forming a connection surface roughness on a main surface (17a) of the connection layer (17), the main surface (17a) facing the movable mass block (12), wherein the connection layer (17) is polysilicon.

[0058] The manufacturing process also includes: anchoring the structural layer (27) to the body (122); forming a dielectric bonding layer (26) on the structural layer (27); bonding a support substrate (25) of semiconductor material to the dielectric bonding layer (26); forming a movable mass block (22) from the body (122); and selectively removing the sacrificial layer (28) to thereby release the movable mass block (22), wherein the movable mass block (22) is constrained to the structural layer (27) so as to be able to oscillate along a direction (D) transverse to the structural layer (27).

[0059] The body (122) comprises single crystal silicon; and wherein the structural layer (27) is electrically conductive.

[0060] The second surface (112a; 27a) of the structural layer (112; 27) has a structural surface roughness that is complementary to the sacrificial surface roughness.

[0061] The structural layer (112; 27) includes polysilicon.

[0062] A process for manufacturing a movable mass (12; 22) on a micro-electromechanical device (10; 20) comprises: forming a sacrificial layer (18; 28) comprising silicon oxide on a bulk layer (13; 122), wherein the sacrificial layer (18; 28) has a first surface (18a; 28a) opposite to the bulk layer (13; 122); forming a transfer layer (19; 119) of a semiconductor material having intrinsic porosity on the first surface (18a; 28a) of the sacrificial layer (18; 28); performing dry etching on the transfer layer (19; 119), thereby partially removing the sacrificial layer (18; 28) through the transfer layer (19; 119) and causing sacrificial surface roughness on the first surface (18a; 28a) of the sacrificial layer (18; 28); removing selected portions of the sacrificial layer (18; 28) using photolithography techniques to obtain a sacrificial surface roughness. Exposing the bulk layer (13; 122); forming a structural layer (112; 27) comprising polysilicon coupled to both the first surface (18a; 28a) of the sacrificial layer (18; 28) and the bulk layer (13; 122), wherein a structural surface roughness (112a; 27a) complementary to the sacrificial surface roughness is generated on the structural layer (112; 27); and wherein the structural layer (112; 27) further forms an anchor (4; 14) in a selected portion of the removed sacrificial layer (18; 28), thereby coupling the structural layer (112; 27) to the bulk layer (13; 122); and selectively removing the sacrificial layer (18; 28) by a wet etching process comprising hydrofluoric acid, thereby releasing a movable mass (12; 22), wherein the movable mass (12; 22) is constrained to the anchor (4; 14).

[0063] The sacrificial surface roughness is defined by a root mean square value between 5 nm and 20 nm.

[0064] The transfer layer (19; 119) comprises polycrystalline silicon having an intrinsic porosity with a full / empty mass ratio lower than 80%.

[0065] The movable mass (12) is formed from a structural layer (112) and oscillates in a direction transverse to a bulk layer (13), the bulk layer comprising a substrate (15) of semiconductor material, a permanent dielectric layer (16) arranged on the substrate (15) and an electrically conductive connection layer (17) arranged on the permanent dielectric layer (16).

[0066] The movable mass (22) is formed from a bulk layer (122) comprising single crystal silicon and oscillates in a direction transverse to the conductive structure layer (27).

[0067] A micro-electromechanical device (10; 20) comprises: a body (13; 122) comprising a semiconductor material and having a main surface (17a; 22a); and a structural layer (112; 27) of semiconductor material having a surface (112a; 27a) facing the main surface (17a; 22a) of the body (13; 122), wherein the main surface (17a; 22a) or the surface (112a; 27a) or both have surface roughness.

[0068] The body (13) comprises: a substrate (15) of semiconductor material; a permanent dielectric layer (16) arranged on the substrate (15); and a conductive connection layer (17) arranged on the permanent dielectric layer (16), the connection layer (17) being defined by a main surface (17a); the device (10) further comprises a movable mass (12) formed from a structural layer (112), the movable mass (12) being defined by a surface (112a), wherein the movable mass (12) is constrained to the connection layer (17) so as to be able to oscillate in a direction (D) transverse to the connection layer (17); and wherein the main surface (17a) has a connection surface roughness and the surface (112a) has a structural surface roughness.

[0069] The device (20) also includes: a dielectric bonding layer (26) arranged on the structural layer (27) and opposite to the surface (27a); a supporting substrate (25) of semiconductor material, which is bonded to the dielectric bonding layer (26); and a movable mass (22) formed from the body (122), the movable mass (22) being defined by a main surface (22a), wherein the movable mass (22) is constrained to the structural layer (27) so as to be able to oscillate along a direction (D) transverse to the structural layer (27); and wherein the structural layer (27) is conductive and the surface (27a) has a structural surface roughness.

[0070] The various embodiments described above can be combined to provide other embodiments. Aspects of the embodiments can be modified, if necessary, to employ the concepts of the various patents, applications and publications to provide other embodiments.

[0071] These and other changes can be made to the embodiments in light of the above detailed description. In general, in the following claims, the terms used should not be understood to limit the claims to the specific embodiments disclosed in the specification and claims, but should be understood to include all possible embodiments within the entire equivalent scope of the rights granted to these claims. Accordingly, the claims are not limited by the present disclosure.

Claims

1. A method for manufacturing a micro-electromechanical device, comprising: forming a sacrificial layer of dielectric material on a body comprising semiconductor material, the sacrificial layer having a first surface opposite to the body; creating a sacrificial surface roughness on the first surface of the sacrificial layer by forming a transfer layer of semiconductor material having intrinsic porosity on the sacrificial layer and partially removing the sacrificial layer through the transfer layer; as well as A structure layer of semiconductor material is formed on the first surface of the sacrificial layer, wherein the structure layer has a second surface, and the second surface is in contact with the first surface of the sacrificial layer. 2 . The manufacturing method according to claim 1 , wherein the sacrificial surface roughness is defined by a root mean square value between 5 nm and 20 nm. 3 . The method of claim 1 , wherein the transfer layer comprises polycrystalline silicon having an intrinsic porosity with a full / empty mass ratio of less than 80%. The manufacturing method according to claim 1 , wherein the sacrificial layer comprises silicon oxide. The manufacturing method according to claim 1 , wherein partially removing the sacrificial layer comprises dry etching the sacrificial layer.

6. The manufacturing method according to claim 1, wherein the body comprises: Substrates of semiconductor materials; a permanent dielectric layer on said substrate; as well as A conductive connecting layer is on the permanent dielectric layer.

7. The manufacturing method according to claim 6, further comprising: anchoring the structural layer to the connecting layer; forming a movable mass from said structural layers; as well as The sacrificial layer is selectively removed, thereby releasing the movable mass, wherein the movable mass is constrained to the connection layer to be able to oscillate in a direction transverse to the connection layer. 8 . The manufacturing method according to claim 7 , further comprising forming connection surface roughness on a main surface of the connection layer, the main surface facing the movable mass, wherein the connection layer is polysilicon.

9. The manufacturing method according to claim 1, further comprising: anchoring the structural layer to the body; forming a dielectric bonding layer on the structural layer; bonding a support substrate of semiconductor material to the dielectric bonding layer; forming a movable mass from said body; as well as The sacrificial layer is selectively removed, thereby releasing the movable mass, wherein the movable mass is constrained to the structural layer to be able to oscillate in a direction transverse to the structural layer.

10. The manufacturing method according to claim 9, wherein the body comprises single crystal silicon; and The structural layer is electrically conductive. 11 . The manufacturing method according to claim 1 , wherein the second surface of the structural layer has a structural surface roughness, and the structural surface roughness is complementary to the sacrificial surface roughness.

12. The manufacturing method according to claim 1, wherein the structural layer comprises polysilicon.

13. A method comprising: The movable mass is fabricated on the MEMS device by the following steps: forming a sacrificial layer comprising silicon oxide on the body layer, wherein the sacrificial layer has a first surface opposite to the body layer; forming a transfer layer of semiconductor material having intrinsic porosity on the first surface of the sacrificial layer; partially removing the sacrificial layer through the transfer layer and creating a sacrificial surface roughness on the first surface of the sacrificial layer; removing selected portions of the sacrificial layer to expose the bulk layer; forming a structural layer comprising polysilicon, the structural layer coupled to both the first surface of the sacrificial layer and the bulk layer, wherein a structural surface roughness complementary to the sacrificial surface roughness is generated on the structural layer; as well as forming anchors in the selected portions with the structural layer to couple the structural layer to the body layer; as well as The sacrificial layer is selectively removed, thereby releasing the movable mass, wherein the movable mass is constrained to the anchor.

14. The manufacturing method of claim 13, wherein the sacrificial surface roughness is defined by a root mean square value between 5 nm and 20 nm.

15. The manufacturing method of claim 13, wherein the transfer layer comprises polysilicon having an intrinsic porosity with a full / empty mass ratio lower than 80%.

16. A manufacturing method according to claim 13, wherein the movable mass is formed from the structural layer, oscillating in a direction transverse to the body layer, the body layer comprising a substrate of semiconductor material, a permanent dielectric layer on the substrate and a conductive connection layer on the permanent dielectric layer. 17 . The manufacturing method according to claim 13 , wherein the movable mass is formed from the body layer comprising single crystal silicon and oscillates in a direction transverse to the conductive structure layer.

18. A micro-electromechanical device, comprising: a body comprising a semiconductor material and having a main surface; as well as A structured layer of semiconductor material having a surface facing the main face of the body, wherein the main face or the surface or both have a surface roughness.

19. The device of claim 18, wherein the body comprises: Substrates of semiconductor materials; a permanent dielectric layer on said substrate; as well as an electrically conductive connection layer on the permanent dielectric layer, the connection layer being bounded by the main surface; as well as The device further comprises a movable mass formed from the structural layer, the movable mass being defined by the surface, wherein the movable mass is constrained to the connection layer so as to be able to oscillate in a direction transverse to the connection layer, and The main face has a connection surface roughness, and the surface has a structure surface roughness.

20. The device of claim 18, further comprising: a dielectric bonding layer on the structural layer and opposite the surface; a support substrate of semiconductor material, the support substrate bonded to the dielectric bonding layer; as well as a movable mass formed from said body, said movable mass being delimited by said main face, wherein the movable mass is constrained to the structural layer so as to be able to oscillate in a direction transverse to the structural layer, and The structured layer is electrically conductive and the surface has a structured surface roughness.

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