CN114105083A

CN114105083A - Micro-electromechanical device and method of forming the same

Info

Publication number: CN114105083A
Application number: CN202010898341.0A
Authority: CN
Inventors: 夏佳杰
Original assignee: Vanguard International Semiconductor Corp
Current assignee: Vanguard International Semiconductor Corp
Priority date: 2020-08-31
Filing date: 2020-08-31
Publication date: 2022-03-01

Abstract

The invention discloses a micro-electromechanical device and a forming method thereof. The substrate has a first surface and a second surface opposite to the first surface. The groove is arranged on the substrate and extends between the first surface and the second surface. The interconnection structure is disposed on the first surface of the substrate and above the trench. The proof mass is disposed on the interconnect structure, wherein the proof mass is partially suspended above the interconnect structure.

Description

Micro-electromechanical device and method of forming the same

Technical Field

The present invention relates to a micro-electromechanical device and a method for forming the same, and more particularly, to a micro-electromechanical device applied to acoustics and a method for forming the same.

Background

Micro-electromechanical system (MEMS) devices are tiny mechanical elements manufactured by conventional semiconductor processes, and mechanical elements with micron dimensions are completed by semiconductor techniques such as depositing or selectively etching material layers. The mems device can operate by using electromagnetic (electromagnetic), electrostrictive (electrostrictive), thermoelectric (pyroelectric), piezoelectric (piezoelectric), or piezoresistive (piezoresistive) effects, and has both electronic and mechanical functions, and thus, is commonly used in microelectronics applications, such as an accelerator (accelerometer), a gyroscope (gyroscope), a mirror (mirror), or an acoustic sensor (acoustic sensor).

In recent years, due to the rapid development of wireless bluetooth (TWS) headsets, mems accelerator products have been used to sense the vibration of sound, bringing a new field of view to acoustic transducers. The micro electro mechanical system speed regulator product is arranged in the wireless Bluetooth earphone, so that the wireless Bluetooth earphone can still effectively capture sound even in the surrounding environment with high noise or more noise. However, since the mems accelerator products are commonly used in the field of mobile phones, the structural design is more biased to be thick and large, so that the design requirement of the miniaturization of the wireless bluetooth headset cannot be satisfied. Thus, there is still a need for a new design of accelerator for use in the acoustic field.

Disclosure of Invention

The invention provides a micro-electromechanical device and a forming method thereof, wherein a proof mass (proof mass) arranged on the micro-electromechanical device is partially arranged above an interconnection structure in a suspension way, thereby the arrangement position of the proof mass can not influence the rigidity of the interconnection structure. Therefore, the size, the mass and the thickness of the mass block can be fully enlarged, so that the sensing sensitivity of the micro-electromechanical device is improved.

To achieve the above objective, an embodiment of the present invention provides a micro-electromechanical device including a substrate, a trench, an interconnection structure, and a mass. The substrate is provided with a first surface and a second surface opposite to the first surface. The groove is arranged in the substrate and extends between the first surface and the second surface. The interconnect structure is disposed on the first surface of the substrate and over the trench. A proof mass is disposed on the interconnect structure, wherein the proof mass is partially suspended above the interconnect structure.

To achieve the above objective, another embodiment of the present invention provides a method for forming a micro-electromechanical device, comprising the following steps. First, a substrate having a first surface and a second surface opposite to the first surface is provided. Then, a groove is formed in the substrate, and the groove extends between the first surface and the second surface. Then, an interconnection structure is formed on the first surface of the substrate, and the interconnection structure is located above the groove. And forming a mass block on the interconnection structure, wherein the mass block is partially suspended above the interconnection structure.

Drawings

FIG. 1 is a schematic cross-sectional view of a micro-electromechanical device (MEMS device) after forming a proof mass (proof mass) according to the present invention.

FIG. 2 is a cross-sectional view of a micro-electromechanical device after trench (cavity) formation in accordance with the present invention.

FIG. 3 is a simulated stress distribution for a suspension region.

FIG. 4 is a cross-sectional view of a micro-electromechanical device after an interconnection structure is formed in accordance with the present invention.

FIG. 5 is a cross-sectional view of a MEMS device after formation of a quality layer in accordance with the present invention.

FIG. 6 is a cross-sectional view of a micro-electromechanical device after trench formation in accordance with the present invention.

FIG. 7 is a cross-sectional view of a MEMS device after forming a proof mass according to the present invention.

FIG. 8 is another cross-sectional view of a MEMS device after forming a proof mass according to the present invention.

Wherein the reference numerals are as follows:

100: substrate

101: first surface

102: second surface

103: groove

103 a: opening of the container

110: oxide layer

111: undercut portion

200: interconnect structure

201: dielectric layer

203: metal layer

205: connecting pad

207: perforation

209: top dielectric layer

210: suspension area

130: mass block

330: mass block

331: base material layer

331 a: base layer

332: hole(s)

333: mass layer

333 a: projection part

350: protective layer

530: mass block

531: base layer

533: mass layer

A: anchor end

F: free end

L: length of

T1, T2: thickness of

Detailed Description

In order that those skilled in the art will be able to more fully understand the present invention, several preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Furthermore, those skilled in the art to which the invention relates will be able to refer to the following embodiments without departing from the spirit of the invention, and will be able to substitute, recombine, and mix features of several different embodiments to accomplish other embodiments.

In the present invention, the description that the first component is formed on or above the second component may mean that the first component is in direct contact with the second component, or that another component is additionally present between the first component and the second component, so that the first component and the second component are not in direct contact. Moreover, various embodiments of the present invention may use repeated reference numerals and/or letters. These repeated use of reference symbols and/or text labels is intended to provide a concise and definite article of discussion and is not intended to indicate any relationship between the various embodiments and/or configurations. In addition, for spatially related descriptive words mentioned in the present invention, for example: the terms "under," "over," "under," "high," "under," "over," "bottom," "top," and the like are used in describing, for convenience of description, the relative relationship of one element or feature to another element or feature(s) in the drawings. In addition to the orientations shown in the drawings, these spatially relative terms are also used to describe possible orientations of the semiconductor device during fabrication, during use, and during operation. For example, when the semiconductor device is rotated 180 degrees, a component that was originally disposed "above" another component becomes disposed "below" the other component. Therefore, as the swing direction of the semiconductor device changes (rotates by 90 degrees or other angles), the spatially related descriptions for describing the swing direction should be interpreted in a corresponding manner.

Although the present invention may have been described using terms such as first, second, third, etc. to describe various elements, components, regions, layers and/or sections, it should be understood that such elements, components, regions, layers and/or sections should not be limited by such terms. These terms are only used to distinguish one element, component, region, layer and/or block from another element, component, region, layer and/or block, and do not denote any order or importance, nor do they denote any order or importance, unless otherwise indicated. Thus, a first element, component, region, layer or block discussed below could be termed a second element, component, region, layer or block without departing from the scope of embodiments of the present invention.

The term "about" or "substantially" as used herein generally means within 20%, preferably within 10%, and more preferably within 5%, or within 3%, or within 2%, or within 1%, or within 0.5% of a given value or range. It should be noted that the amounts provided in the specification are approximate amounts, i.e., the meaning of "about" or "substantially" may be implied without specifically stating "about" or "substantially".

Referring to fig. 1 to 3, schematic diagrams of a method for forming a micro-electromechanical device according to an embodiment of the invention are shown. First, as shown in fig. 1, a substrate 100, such as a bulk silicon substrate (bulk silicon substrate), is provided, and the substrate 100 includes, but is not limited to, monocrystalline silicon, polycrystalline silicon, amorphous silicon, or other suitable materials. In one embodiment, the substrate 100 has a suitable thickness T1, such as about 400 micrometers (μm) to about 500 μm, but not limited thereto. One of ordinary skill in the art will readily appreciate that the thickness of the substrate 100 may be further adjusted according to the predetermined depth of the subsequently formed trench to meet the actual product requirements.

The substrate 100 has two opposite surfaces, such as a first surface 101 and a second surface 102 opposite to the first surface 101 shown in fig. 1, and an oxide layer 110 and an interconnect structure 200 are sequentially formed on the first surface 101 of the substrate 100. The oxide layer 110 includes, for example, silicon oxide (SiO) or silicon dioxide (SiO)₂) The interconnect structure 200 may be any suitable semiconductor structure formed by conventional semiconductor processes, such as deposition and/or selective etching of material layers. The interconnect structure 200 may include at least a bottom electrode (not shown), a top electrode (not shown) disposed on the bottom electrode, and a piezoelectric layer (not shown) disposed between the bottom electrode and the top electrode. In an embodiment, the interconnect structure 200 further includes at least one dielectric layer 201 stacked on the first surface 101, at least one metal layer 203 embedded in the at least one dielectric layer 201, and at least one connection pad 205 electrically connected to the at least one metal layer 203, as shown in fig. 1, wherein the at least one dielectric layer 201 includes a dielectric material such as silicon nitride (SiN) or silicon oxynitride (SiON), and the at least one metal layer 203 includes a metal material such as copper (Cu), molybdenum (Mo), tungsten (W), or aluminum (Al), but not limited thereto.

It is noted that the interconnect structure 200 further includes a via 207 disposed in a suspension region 210, whereby a structure disposed in the suspension region 210 may be partially separated from the substrate 100 in a subsequent process to form a suspended structure (not shown). The suspension structure includes, for example, the top electrode, the piezoelectric layer, and the bottom electrode stacked in the interconnect structure 200 from top to bottom, so as to be capable of vibrating at a specific frequency when the mems device is operating. In the present embodiment, the suspension structure may include a cantilever (cantilever), a diaphragm (diaphragm), and the like, but is not limited thereto.

Next, a proof mass 130 is formed on the interconnect structure 200 such that the proof mass 130 is located above the suspended structure in the suspended region 210. The mass 130 may comprise any suitable material with a high mass density (mass density), such as, but not limited to, aluminum copper (AlCu), copper, gold (Au), platinum (Pt), molybdenum (mo), silicon (Si), etc. Preferably, the mass 130 is disposed near the through hole 207, and the length L of the mass 130 is, for example, about 1/2 to 1/3 of the length of the suspension region 210, so as to avoid the placement of the mass 130 in a stress concentration region of the interconnect structure 200, which affects the stiffness thereof. The thickness of the mass 130 is preferably, but not limited to, about 1 to 3 microns. In one embodiment, the proof mass 130 is formed within a top dielectric layer 209 of the interconnect structure 200, for example, the proof mass 130 may be selectively disposed to partially protrude above the top surface of the top dielectric layer 209, as shown in FIG. 1, to achieve greater mass. In another embodiment, the mass (not shown) may not protrude from the top surface of the top dielectric layer 209, but may be coplanar with the top surface of the top dielectric layer 209.

Then, as shown in fig. 2, a trench 103 is formed from the back side of the substrate 100, i.e., the side where the second surface 102 is located. Specifically, a mask layer (not shown) is formed on the second surface 102 to define the position and size of the trench 103, and an etching process is performed through the mask layer to remove a certain amount of the substrate 100 until the underlying oxide layer 110 is partially exposed. The shielding layer has an opening preferably corresponding to the suspended structure disposed in the suspended region 210, and the size of the opening is preferably equal to the predetermined size of the trench 103, for example, but not limited to, about 100 microns to 150 microns. It should be readily understood by those skilled in the art that the size of the trench 103 is not limited to the foregoing, and can be further adjusted according to the actual product requirements.

In other words, the trench 103 is processed by using the oxide layer 110 as an etch stop layer, such that the trench 103 may extend between two opposite surfaces (the first surface 101 and the second surface 102) of the substrate 100, thereby facing the suspended structure located in the suspended region 210 of the interconnect structure 200 disposed on the first surface 101. Thus, the trench 103 may have a depth equal to the thickness T1 of the substrate 100, and the trench 103 has an opening 103a adjacent to the bottom surface of the overhang region 210, as shown in fig. 2. Thereafter, another etching process is performed to remove the exposed portion of the oxide layer 110, so that the bottom surface of the suspending region 210 of the underlying interconnect structure 200 can be exposed and interconnected with the trench 103, as shown in fig. 2. Note that, during the another etching process, the sidewalls of the remaining oxide layer 110 may also be slightly removed to form an undercut (under cut) portion 111 adjacent to the opening 103a of the trench 103.

In addition, in an embodiment, a protection layer (not shown) may be additionally formed on the interconnect structure 200 before the trench 103 is formed to protect the elements disposed in the interconnect structure 200, wherein the protection layer may comprise silicon oxide or silicon dioxide. Then, after the trench 103 is formed and the exposed portion of the oxide layer 110 is removed, the protective layer is completely removed to release the suspension structure in the suspension region 210 of the interconnect structure 200. In this case, since the hanging region 210 of the interconnect structure 200 has the through hole 207 therein, one end (also referred to as a free end F) of the hanging structure is not connected to the substrate 100 and is in a floating state, and the other end (also referred to as an anchor end a) of the hanging structure is still connected to the substrate 100 and the remaining oxide layer 110 disposed on the substrate 100, as shown in fig. 2.

Therefore, the micro-electromechanical device in the first embodiment of the invention can be formed. In the present embodiment, the mems device comprises the suspension structure disposed in the suspension region 210 of the interconnect structure 200, the trench 103 and the mass 130, thereby acting as a mems accelerator, and the suspension structure is tuned by the mass 130 to have a resonant frequency corresponding to the audio frequency range to be sensed, and by the piezoelectric layer disposed in the suspension structure to generate a corresponding vibration when receiving an acoustic or electrical signal. It is worth noting thatWhen the suspension structure vibrates, the suspension structure is deformed by pressure and vibration, and then the suspension structure generates piezoelectric reaction. Referring to fig. 3, the stress distribution pattern is shown, wherein the intensity of the stress distribution in the suspension region 210 is represented by the density of the dot-shaped mesh bottom. Generally, most of the stress will be concentrated at the other end (i.e., anchor end a) of the suspension structure, as shown in fig. 3. Therefore, the mass 130 of the present embodiment is disposed adjacent to the end (i.e., the free end F) of the suspension structure, i.e., in a region with a smaller stress distribution. With this arrangement, the mass 130 of the present embodiment does not affect the stiffness of the suspension structure located in the suspension region 210. According to the following formula (I), the minimum sensing signal (a) of the MEMS device_min) The mass of the mass block 130 is directly related to the mass of the mass block 130, so that the micro electro mechanical device provided with the mass block 130 in the embodiment can be applied to the wireless bluetooth headset, thereby assisting the voice vibration of the microphone. Formula (I):

wherein, κ_BBoltzmann's constant (Boltzmann's constant); t is the absolute temperature; omega₀Is the resonant frequency; m is_iIs the mass of the sensor; q is a mass coefficient.

It will also be appreciated by those of ordinary skill in the art that the microelectromechanical device and method of forming the same of the present invention is not limited to the foregoing, but may have other aspects or variations. For example, although the above-mentioned process is described as an implementation mode in which the mems device is formed on a bulk silicon substrate, the actual process is not limited thereto, and alternatively, the operation may be performed on a silicon-on-insulator (SOI) substrate. Other embodiments or variations of the microelectromechanical device of the invention and methods of forming the same will be described below. For simplicity, the following description mainly refers to the differences of the embodiments, and the description of the same parts is not repeated. In addition, the same elements in the embodiments of the present invention are denoted by the same reference numerals to facilitate the comparison between the embodiments.

In another embodiment of the present invention, a micro-electromechanical device and a method for forming the same are disclosed, wherein the minimum sensing signal (a) of the micro-electromechanical device is_min) The mass of the mass is positively correlated with the mass of the suspension structure in the suspension region 210, and the mass of the mass is correlated with the rigidity of the suspension structure, so that the mass is more optimized (heavier) but the rigidity of the suspension structure is not affected. Referring to fig. 4 to 7, schematic diagrams illustrating a method for forming a micro-electromechanical device according to a second embodiment of the present invention are shown. The forming method of the present embodiment is substantially similar to the previous embodiments in steps, and the description of the similar parts is omitted. The main difference between the present embodiment and the previous embodiments is that the mass 330 of the present embodiment is partially suspended above the interconnect structure 200.

As shown in fig. 4, the substrate 100 also has a first surface 101 and a second surface 102, and an oxide layer 110 and an interconnect structure 200 are sequentially formed on the first surface 101 of the substrate 100. It should be noted that the detailed features of the substrate 100, the oxide layer 110 and the interconnect structure 200 in the present embodiment are substantially the same as those in the previous embodiment, and are not repeated. Next, a base material layer (base material layer)331 is formed on the top surface of the top dielectric layer 209, and the base material layer 331 further fills the through hole 207, as shown in fig. 4. In one embodiment, the base material layer 331 includes, but is not limited to, silicon oxide or silicon dioxide.

Then, as shown in fig. 5, at least one opening is formed in the base material layer 331 and the top dielectric layer 209, wherein the at least one opening is located within the suspension region 210. Preferably, the at least one opening is formed in the suspension structure adjacent to the aperture 207. In the present embodiment, an opening is formed, and the opening may have a ring-shaped appearance when viewed from a top view (not shown), and may present two holes 332 separated from each other when viewed from a cross-sectional view, as shown in fig. 5, but the arrangement and the aspect of the opening are not limited thereto. That is, the two holes 332 may be connected to each other when viewed from a top-down view, but not limited thereto. In another embodiment, various numbers of openings may be formed adjacent to the through-hole 207 depending on actual process requirements. Thereafter, a mass layer 333 is formed on the base material layer 331, and the mass layer 333 is also formed in the range of the suspension region 210, and further filled in the hole 332 to form a protrusion 333a, so that the protrusion 333a can surround a part of the base material layer 331, as shown in fig. 5. The formation of the mass layer 333 may include steps of first forming a mass material layer (not shown) on the base material layer 331 so that the mass material layer entirely covers all surfaces of the base material layer 331, and then patterning the mass material layer to form the mass layer 333 shown in fig. 5. In one embodiment, mass layer 333 comprises any suitable material having a relatively high mass density, such as, but not limited to, aluminum copper, gold, platinum, molybdenum, or silicon. It should be noted that the mass layer 333 may have a relatively large thickness, such that the overall thickness T2 of the mass layer 333 and the underlying base material layer 331 may be about 5 microns to 15 microns, preferably 10 microns, but not limited thereto. In addition, the thickness of the mass layer 333 may be adjusted individually according to the thickness of the connection pads on the surface of the interconnect structure 200.

As shown in fig. 6, a trench 103 is formed from the backside of the substrate 100, i.e., the side where the second surface 102 is located. Specifically, before forming the trench 103, a protection layer 350 is formed on the interconnect structure 200 to cover the quality layer 333, the base material layer 331 and the interconnect structure 200, thereby protecting the underlying devices. The passivation layer 350 may comprise silicon oxide, silicon dioxide, or other materials with the same or similar etching selectivity ratio as the underlying base material layer 331. Then, a mask layer (not shown) is formed on the second surface 102 to define the location and size of the trench 103, and an etching process, such as an anisotropic dry etching process, is performed from the backside of the substrate 100 through the mask layer to remove a portion of the substrate 100 until the underlying oxide layer 110 is partially exposed. In one embodiment, the shielding layer has an opening, which preferably corresponds to the suspension structure disposed in the suspension region 210, and the size of the opening is preferably equal to the predetermined size of the trench 103, for example, but not limited thereto, about 100 to 150 μm.

Thereby, the trench 103 is formed in the substrate 100 by using the oxide layer 110 as an etch stop layer, such that the trench 103 may extend between two opposite surfaces (the first surface 101 and the second surface 102) of the substrate 100 and have a depth equal to the thickness T1 of the substrate 100, and further, the trench 103 may be aligned to a suspended structure in a suspended region 210 of the interconnect structure 200 disposed on the first surface 101, and the trench 103 has an opening 103a adjacent to a bottom surface of the suspended region 210, as shown in fig. 6.

Thereafter, as shown in fig. 7, another etching process, such as an isotropic wet etching process, is performed to remove the portion of the oxide layer 110 exposed from the trench 103, so that the bottom surface of the underlying suspension region 210 may be partially exposed and may communicate with the trench 103. It is noted that, during the further etching process, the sidewalls of the remaining oxide layer 110 may also be slightly removed to form an undercut portion 111 adjacent to the opening 103a of the trench 103. The protection layer 350 and the base material layer 331 are then removed, thereby releasing the suspended structure within the suspended region 210 of the interconnect structure 200. Thus, one end (also referred to as free end F) of the suspension structure is not connected to the substrate 100 and is in a suspended state, and the other end (also referred to as anchor end a) of the suspension structure is still connected to the substrate 100, so that when the mems device operates to vibrate the suspension structure, more stress is concentrated on the anchor end a of the suspension structure, and less stress is concentrated on the free end F of the suspension structure.

In one embodiment, the protection layer 350 and the base material layer 331 may be selectively removed when removing a portion of the exposed oxide layer 110, but is not limited thereto. In another embodiment, the protection layer 350 and the base material layer 331 may be additionally removed by another isotropic wet etching process. Note that, when the protection layer 350 and the base material layer 331 are removed, the protection layer 350 and most of the base material layer 331 are completely removed, and only the portion of the base material layer 331 surrounded by the protrusion 333a of the mass layer 333 is left, so that the base layer 331a shown in fig. 7 can be formed. Thereby, the base layer 331a and the mass layer 333 can jointly form the mass 330 of the present embodiment. The mass 330 of the present embodiment includes a double-layer structure, wherein the base layer 331a and the protrusion 333a surrounding the base layer 331a are disposed at the bottom layer of the double-layer structure, and the mass layer 333 disposed above the base layer 331a and the protrusion 333a is disposed at the top layer of the double-layer structure. It should be noted that only the bottom layer (the base layer 331a and the protrusion 333a) of the mass 330 is directly disposed on the suspension structure of the suspension region 210 and is disposed adjacent to the free end F of the suspension structure, and the top layer (the mass layer 333) of the mass 330 may further extend from the free end F of the suspension structure to the anchor end a, so that one end of the top layer may be suspended above the anchor end a, as shown in fig. 7.

Thus, the micro-electromechanical device according to the second embodiment of the present invention can be formed. In this embodiment, the mems device comprises the suspension structure disposed in the suspension region 210 of the interconnect structure 200, the trench 103 and the mass 330, which also serves as a mems accelerator, and the suspension structure is tuned by the mass 330 to have a resonant frequency corresponding to the audio frequency range to be sensed by the piezoelectric layer disposed in the suspension structure to vibrate when receiving acoustic or electrical signals. It should be noted that the mass 330 of the present embodiment includes a double-layer structure, which is composed of a bottom layer (the base layer 331a and the protrusion 333a) and a top layer (the mass layer 333), such that the top layer can extend from the free end F to the anchor end a of the suspension structure, and the mass layer 330 of the present embodiment has the advantages of a larger thickness T2, a larger size, and a larger mass. The thickness T2 of the mass 330 is, for example, about 5 to 10 times the thickness of the mass 130 in the first embodiment, such as about 5 to 15 microns, preferably 10 microns, but not limited thereto. In addition, the mass 330 of the present embodiment has only the bottom layer (the base layer 331a and the protrusion 333a) directly disposed on the suspension structure in the region with less stress distribution in the suspension structure (i.e. the region near the free end F), while the top layer (the mass layer 333) of the mass 330 may be disposed over the anchor end a with one end suspended without directly contacting the stress concentration region of the suspension structure. Thus, the mass 330 of the present embodiment having a greater thickness, a greater size, and a greater mass does not affect the stiffness of the suspension structure located within the suspension region 210, thereby providing more optimal sensing sensitivity. Therefore, the micro electro-mechanical device having the mass 330 can be applied to a wireless bluetooth headset, thereby assisting the voice vibration of the microphone.

Referring to fig. 8, a schematic diagram of a method for forming a micro-electromechanical device according to a third embodiment of the invention is shown. The forming method of the present embodiment is substantially similar to the previous embodiments in steps, and the description of the similar parts is omitted. The main difference between this embodiment and the previous embodiments is that the mass layer 533 of the mass 530 is only located at the top layer of the double-layer structure, and does not extend downward and surround the base layer 531 at the bottom layer of the double-layer structure.

Specifically, the mass layer 533 of the present embodiment is directly formed on the base material layer 331 as shown in fig. 4. Then, similar to the process of the second embodiment, after the protection layer 350 is formed, the trench 103 is formed, and the oxide layer 110, the protection layer 350 and the base material layer 331 are removed by an isotropic wet etching process. It should be noted that when the base material layer in the present embodiment is removed by the isotropic wet etching process, the etching conditions such as the etching rate and the etching time are further controlled to form the base layer 531 as shown in fig. 8, so that the base layer 531 is only formed in the region with less stress distribution (i.e., the region near the free end F) without removing all of the base material layer. In this case, the base layer 531 and the mass layer 533 may also jointly form the mass 530 of the present embodiment, and the mass 530 is also disposed adjacent to the free end F of the suspension structure without affecting the stiffness of the suspension structure in the suspension region 210.

Thus, the mems device in the third embodiment of the present invention, which also includes the suspension structure disposed in the suspension region 210 of the interconnect structure 200, the trench 103 and the mass 530, can also be used as a mems accelerator, and can vibrate when receiving an acoustic or electrical signal through the piezoelectric layer disposed in the suspension structure, and adjust the suspension structure through the mass 530, so that the suspension structure has a resonant frequency corresponding to the audio frequency range to be sensed. It should be noted that the mass 530 of the present embodiment also has a larger size, a larger mass and a larger thickness T2, and the thickness T2 of the mass 530 is, for example, about 5 to 15 microns, but not limited thereto. Also, the mass 530 having a larger thickness, a larger size, and a larger mass in this embodiment does not affect the stiffness of the suspension structure located in the suspension region 210, thereby providing more optimized sensing sensitivity. Therefore, the micro-electromechanical device of the present invention having the mass 530 can be applied to a wireless bluetooth headset, thereby assisting the voice vibration of the microphone.

In general, the present invention provides a proof mass having a two-layer structure, a bottom layer of the mass being disposed directly on a suspension structure within a suspension region and within a region of the suspension structure having a reduced stress distribution, and a top layer of the mass being disposed on the bottom layer. Thus, one end of the top layer of the mass is directly disposed on the bottom layer, and the other end of the top layer is further extended and suspended above the suspension structure without directly contacting the suspension structure in the suspension region. Therefore, the invention can fully enlarge the size, the mass, the thickness and the like of the mass block on the premise of avoiding influencing the rigidity of the suspension structure, thereby being beneficial to improving the sensing sensitivity of the micro-electro-mechanical device. Therefore, the micro-electromechanical device with the mass block can be applied to a wireless Bluetooth headset, so that the voice vibration of the microphone is assisted. In addition, it should be readily understood by those skilled in the art that although the foregoing embodiments of the present invention have been described with reference to the mass having a double-layer structure, the actual structure of the mass is not limited thereto. In another embodiment, a mass block having a multi-layer structure may be selectively formed, and may also be partially suspended above the stress concentration region of the suspension structure, so as to avoid affecting the rigidity of the suspension structure while improving the sensing sensitivity of the mems device.

The above description is only a preferred embodiment of the present invention, and all the equivalent changes and modifications made by the claims of the present invention should fall within the protection scope of the present invention.

Claims

1. A microelectromechanical device, comprising:

a substrate having a first surface and a second surface opposite to the first surface;

a trench disposed in the substrate, the trench extending between the first surface and the second surface;

an interconnect structure disposed on the first surface of the substrate and over the trench; and

a proof mass disposed on the interconnect structure, wherein the proof mass is partially suspended above the interconnect structure.

2. The microelectromechanical device of claim 1, wherein the proof mass comprises a base layer disposed directly on the interconnect structure and a mass layer disposed on the base layer.

3. The microelectromechanical device of claim 2, characterized in that one end of the mass layer is located on the base layer and the other end of the mass layer is suspended from the interconnect structure.

4. The microelectromechanical device of claim 2, characterized in that the mass layer further comprises a protrusion, said protrusion surrounding a sidewall of the base layer.

5. The micro-electromechanical device according to claim 4, wherein the protrusion directly contacts the interconnect structure.

6. The microelectromechanical device of claim 2, wherein the interconnect structure further comprises a hanging region corresponding to the trench, a first end of the hanging region being directly connected to the substrate, and a second end of the hanging region not being directly connected to the substrate.

7. The microelectromechanical device of claim 6, characterized in that the base layer is disposed adjacent to the second end of the suspension region.

8. The microelectromechanical device of claim 6, wherein the mass layer extends from the first end of the suspension region to the second end of the suspension region.

9. The microelectromechanical device of claim 1, further comprising an oxide layer disposed between the interconnect structure and the substrate.

10. The microelectromechanical device of claim 1, wherein the trench has a thickness that is the same as a thickness of the substrate.

11. The microelectromechanical device of claim 1, characterized in that at least one end of the mass is suspended above the interconnect structure.

12. A method of forming a micro-electromechanical device, comprising:

providing a substrate, wherein the substrate is provided with a first surface and a second surface opposite to the first surface;

forming a trench in the substrate, the trench extending between the first surface and the second surface;

forming an interconnection structure on the first surface of the substrate, wherein the interconnection structure is positioned above the groove; and

forming a mass on the interconnect structure, wherein the mass is partially suspended above the interconnect structure.

13. The method of forming a microelectromechanical device of claim 12 wherein the mass is formed after the trench is formed.

14. The method of forming a microelectromechanical device of claim 12, wherein the forming of the proof mass further comprises:

forming a base layer on the interconnect structure; and

a mass layer is formed.

15. The method of forming a microelectromechanical device of claim 14, further comprising: forming a base material layer on the interconnection structure;

forming the quality layer on the base material layer before the trench is formed; and

after the trench is formed, partially removing the base material layer to form the base layer.

16. The method of forming a microelectromechanical device of claim 15, further comprising: forming a via in the base layer before the trench is formed; and

forming the mass layer, wherein the mass layer comprises a protruding part arranged in the through hole.

17. The method of forming a micro-electromechanical device according to claim 16, wherein the protrusion surrounds a sidewall of the base layer and directly contacts the interconnect structure.

18. The method of forming a microelectromechanical device of claim 12, further comprising: forming an oxide layer between the interconnect structure and the substrate; and

after the groove is formed, the oxide layer is partially removed to communicate the groove and the interconnection structure.

19. The method of forming a microelectromechanical device of claim 12, wherein the forming of the trench comprises:

removing the substrate from the second surface portion.

20. The method of forming a microelectromechanical device of claim 12, characterized in that at least one end of the proof mass is suspended above the interconnect structure.