Microelectromechanical device and method of forming the same

Abstract

The present invention discloses a microelectromechanical device and a method for forming the same. The microelectromechanical device includes a substrate, a trench, an interconnect structure, and a mass. The substrate has a first surface and a second surface opposite to the first surface. The trench is formed 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 above the trench. The mass is disposed on the interconnect structure, wherein the mass is partially suspended above the interconnect structure.

Description

Technical Field

[0001] The present invention relates to a microelectromechanical device and a method for forming the same, and more particularly to a microelectromechanical device applied to acoustics and a method for forming the same. Background Art

[0002] Micro-electromechanical system (MEMS) devices are tiny mechanical components fabricated using existing semiconductor processes. Mechanical components with micron-scale dimensions are completed through semiconductor technologies such as depositing or selectively etching material layers. MEMS devices can operate using electromagnetic, electrostrictive, thermoelectric, piezoelectric, or piezoresistive effects, combining both electronic and mechanical functions. Therefore, they are commonly used in microelectronics applications such as accelerometers, gyroscopes, mirrors, or acoustic sensors.

[0003] In recent years, due to the rapid development of true wireless stereo (TWS) earphones, MEMS accelerometer products can be used to sense sound vibrations, bringing new perspectives to acoustic transducers. By placing MEMS accelerometer products inside the TWS earphones, the earphones can effectively capture sound even in noisy environments. However, since MEMS accelerometer products are currently more commonly used in the mobile phone field, their structural designs tend to be thick and large, unable to meet the miniaturization design requirements of TWS earphones. Thus, there is still a need for a newly designed accelerometer for acoustic applications. Summary of the Invention

[0004] The present invention provides a microelectromechanical device and a method for forming the same. The proof mass of the microelectromechanical device is partially suspended above the interconnection structure. Thus, the position of the mass will not affect the stiffness of the interconnection structure. In this way, the size, mass, and thickness of the mass in the present invention can be fully enlarged to improve the sensing sensitivity of the microelectromechanical device.

[0005] To achieve the above object, an embodiment of the present invention provides a microelectromechanical device, including a substrate, a trench, an interconnection structure, and a proof mass. The substrate has a first surface and a second surface opposite to the first surface. The trench is disposed in 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 interconnection structure, wherein the proof mass is partially suspended above the interconnection structure.

[0006] To achieve the above object, another embodiment of the present invention provides a method for forming a microelectromechanical device, including the following steps. First, a substrate is provided, the substrate having a first surface and a second surface opposite to the first surface. Then, a trench is formed in the substrate, the trench extending between the first surface and the second surface. Next, an interconnection structure is formed on the first surface of the substrate, the interconnection structure being above the trench. After that, a proof mass is formed on the interconnection structure, wherein the proof mass is partially suspended above the interconnection structure. Description of the Drawings

[0007] Figure 1 It is a cross-sectional schematic diagram of a microelectromechanical device (MEMS device) of the present invention after forming a proof mass.

[0008] Figure 2 It is a cross-sectional schematic diagram of a microelectromechanical device of the present invention after forming a cavity.

[0009] Figure 3 It is a simulation schematic diagram of the stress distribution in a suspended area.

[0010] Figure 4 It is a cross-sectional schematic diagram of a microelectromechanical device of the present invention after forming an interconnection structure.

[0011] Figure 5 It is a cross-sectional schematic diagram of a microelectromechanical device of the present invention after forming a mass layer.

[0012] Figure 6 It is a cross-sectional schematic diagram of a microelectromechanical device of the present invention after forming a trench.

[0013] Figure 7 It is a cross-sectional schematic diagram of a microelectromechanical device of the present invention after forming a proof mass.

[0014] Figure 8 It is another cross-sectional schematic diagram of a microelectromechanical device of the present invention after forming a proof mass.

[0015] Among them, the reference numerals are explained as follows:

[0016] 100: Substrate

[0017] 101: First surface

[0018] 102: Second surface

[0019] 103: Groove

[0020] 103a: Opening

[0021] 110: Oxide layer

[0022] 111: Undercut portion

[0023] 200: Interconnection structure

[0024] 201: Dielectric layer

[0025] 203: Metal layer

[0026] 205: Connection pad

[0027] 207: Through hole

[0028] 209: Top dielectric layer

[0029] 210: Suspended area

[0030] 130: Mass

[0031] 330: Mass

[0032] 331: Base material layer

[0033] 331a: Base layer

[0034] 332: Hole

[0035] 333: Mass layer

[0036] 333a: Protrusion

[0037] 350: Protective layer

[0038] 530: Mass

[0039] 531: Base layer

[0040] 533: Mass layer

[0041] A: Anchor end

[0042] F: Free end

[0043] L: Length

[0044] T1, T2: Thickness Detailed implementation manners

[0045] To enable those of ordinary skill in the art to which the present invention pertains to further understand the present invention, several preferred embodiments of the present invention are specifically listed below, and in conjunction with the accompanying drawings, the composition and the effects to be achieved of the present invention are described in detail. Moreover, those of ordinary skill in the art to which the present invention pertains can, without departing from the spirit of the present invention, refer to the following embodiments and replace, recombine, and mix the features in several different embodiments to complete other embodiments.

[0046] In the present invention, the description of "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 it may mean that "there are other components between the first component and the second component", so that the first component and the second component are not in direct contact. In addition, various embodiments in the present invention may use repeated element symbols and / or text notations. The use of these repeated element symbols and text notations is to make the description more concise and clear, rather than to indicate the relevance between different embodiments and / or configurations. Additionally, regarding the spatial-related descriptive terms mentioned in the present invention, such as: "beneath", "above", "low", "high", "below", "above", "under", "on", "bottom", "top" and similar terms, for the convenience of description, their usage is to describe the relative relationship between one component or feature and another (or multiple) component or feature in the drawings. Except for the orientation shown in the drawings, these spatial-related terms are also used to describe the possible orientations during the manufacturing process, use, and operation of the semiconductor device. For example, when the semiconductor device is rotated 180 degrees, a certain component originally disposed "above" other components will then be disposed "below" other components. Therefore, as the orientation of the semiconductor device changes (rotated 90 degrees or other angles), the spatial-related descriptions used to describe its orientation should also be interpreted in a corresponding manner.

[0047] Although the present invention uses terms such as first, second, third, etc. to describe various elements, components, regions, layers, and / or sections, it should be understood that these elements, components, regions, layers, and / or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, and / or section from another element, component, region, layer, and / or section, and they do not imply and represent any previous ordinal number of the element itself, nor the arrangement order of one element and another element, or the order in the manufacturing method. Therefore, without departing from the scope of the specific embodiments of the present invention, the first element, component, region, layer, or section discussed below can also be referred to by terms such as the second element, component, region, layer, or section.

[0048] As used herein, the terms "about" or "substantially" generally mean within 20%, preferably within 10%, more preferably within 5%, or 3%, or 2%, or 1%, or 0.5% of a given value or range. It should be noted that the quantities provided in the specification are approximate quantities, that is, the meaning of "about" or "substantially" may still be implied even without specific mention of "about" or "substantially".

[0049] Please refer to Figures 1 to 3 shown, which is a schematic diagram showing the forming method of the microelectromechanical device in the first embodiment of the present invention. First, as Figure 1 shown, a substrate 100 is provided, such as a bulk silicon substrate. The substrate 100 may include, for example, single-crystalline silicon, polycrystalline silicon, amorphous silicon, or other suitable materials, but is not limited thereto. In one embodiment, the substrate 100 has a suitable thickness T1, for example, about 400 micrometers (μm) to 500 micrometers, but is not limited thereto. Those of ordinary skill in the art should easily understand that, in order to meet the requirements of actual products, the thickness of the substrate 100 can be further adjusted according to the predetermined depth of the trenches formed subsequently.

[0050] The substrate 100 has two opposite surfaces, such as Figure 1 shown, the first surface 101 and the second surface 102 opposite to the first surface 101. 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 may include, for example, silicon oxide (SiO) or silicon dioxide (SiO2), and the interconnect structure 200 may be any suitable semiconductor structure formed by using existing semiconductor processes such as depositing and / or selectively etching material layers. The interconnect structure 200 may include at least one 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 one 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 buried 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 Figure 1As shown, at least one dielectric layer 201 includes, for example, dielectric materials such as silicon nitride (SiN) or silicon oxynitride (SiON), and at least one metal layer 203 includes, for example, metal materials such as copper (Cu), molybdenum (Mo), tungsten (W), or aluminum (Al), but is not limited thereto.

[0051] It should be noted that the interconnect structure 200 further includes a via 207 disposed within a suspension region 210. Thereby, a structure disposed within the suspension region 210 can be partially separated from the substrate 100 in a subsequent process to form a suspended structure (not shown). The suspended structure includes, for example, the top electrode, the piezoelectric layer, and the bottom electrode stacked in sequence from top to bottom within the interconnect structure 200, and can thus vibrate at a specific frequency when the MEMS device operates. In this embodiment, the suspended structure can include structures such as a cantilever, a diaphragm, etc., but is not limited thereto.

[0052] Next, a mass 130 is formed on the interconnect structure 200 such that the mass 130 is located above the suspended structure in the suspension region 210. The mass 130 can include any suitable material with a relatively high mass density, such as aluminum copper (AlCu), copper, gold (Au), platinum (Pt), molybdenum, or silicon (Si), etc., but is not limited thereto. Preferably, the mass 130 is disposed near the via 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 prevent the setting position of the mass 130 from falling within the stress concentration region of the interconnect structure 200 and affecting its stiffness. The thickness of the mass 130 is preferably about 1 to 3 microns, but is not limited thereto. In one embodiment, the mass 130 is formed within a top dielectric layer 209 of the interconnect structure 200. For example, when the mass 130 is disposed, it can be selected to partially protrude from the top surface of the top dielectric layer 209, as Figure 1 shown, to obtain a larger mass. In another embodiment, when the mass (not shown) is disposed, it can also be selected not to protrude from the top surface of the top dielectric layer 209, but to be coplanar with the top surface of the top dielectric layer 209.

[0053] Then, as Figure 2As shown, a groove 103 is formed on the dorsal side of the substrate 100, i.e., the side where the second surface 102 is located. Specifically, a shielding layer (not shown) is first formed on the second surface 102 to define the position and size of the groove 103, and then an etching process is carried out through the shielding layer to remove a certain degree of the substrate 100 until a part of the underlying oxide layer 110 is exposed. The shielding layer has an opening, and the opening preferably corresponds to the suspension structure disposed in the suspension area 210, and the size of the opening is preferably equal to the predetermined size of the groove 103, for example, about 100 microns to 150 microns, but not limited thereto. Those of ordinary skill in the art should easily understand that the size of the groove 103 is not limited to the foregoing and can be further adjusted according to the actual product requirements.

[0054] In other words, the process of the groove 103 is carried out by using the oxide layer 110 as an etching stop layer, so that the groove 103 can extend between two opposite surfaces (the first surface 101 and the second surface 102) of the substrate 100, and then to the suspension structure located in the suspension area 210 of the interconnect structure 200 disposed on the first surface 101. Thus, the groove 103 can have a depth equal to the thickness T1 of the substrate 100, and the groove 103 has an opening 103a at the bottom surface adjacent to the suspension area 210, as Figure 2 shown. Then, another etching process is carried out to remove the exposed part of the oxide layer 110, so that the bottom surface of the suspension area 210 of the underlying interconnect structure 200 can be exposed and communicate with the groove 103, as Figure 2 shown. It should be noted that when carrying out this another etching process, the side walls of the remaining oxide layer 110 can also be slightly removed together to form an under cut part 111 at the opening 103a adjacent to the groove 103.

[0055] In addition, in an embodiment, it is also possible to optionally form a protection layer (not shown) on the interconnect structure 200 before forming the groove 103 to protect the components disposed in the interconnect structure 200. The protection layer includes, for example, materials such as silicon oxide or silicon dioxide. Then, after the groove 103 is formed and the exposed part of the oxide layer 110 is removed, the protection layer is completely removed to release the suspension structure located in the suspension area 210 of the interconnect structure 200. In this case, since there are perforations 207 in the suspension area 210 of the interconnect structure 200, one end (also referred to as the free end F) of the suspension structure is not connected to the substrate 100 and is in a suspended state, while the other end (also referred to as the anchor end A) of the suspension structure is still connected to the substrate 100 and the remaining oxide layer 110 disposed on the substrate 100, as Figure 2 shown.

[0056] Thus, the MEMS device in the first embodiment of the present invention can be formed. In this embodiment, the MEMS device includes a suspension structure, a trench 103, and a mass 130 disposed in the suspension area 210 of the interconnect structure 200. Therefore, it can be used as a MEMS accelerator. When receiving an acoustic wave or an electrical signal, the piezoelectric layer disposed in the suspension structure generates corresponding vibrations, and the suspension structure is adjusted by the mass 130 so that the suspension structure has a resonance frequency that can meet the required sensed audio range. It should be noted that when the suspension structure vibrates, pressure and vibration cause the suspension structure to deform, and then the suspension structure generates a piezoelectric reaction. Please refer to Figure 3 the stress distribution pattern shown, where the intensity of the stress distribution in the suspension area 210 is represented by the density of the dot-mesh bottom. Generally, most of the stress will concentrate at the other end (i.e., the anchor end A) of the suspension structure, as Figure 3 shown. Therefore, the mass 130 in this embodiment is disposed at a position adjacent to the end (i.e., the free end F) of the suspension structure, that is, in an area with a smaller stress distribution. With this setting, the mass 130 in this embodiment will not affect the stiffness of the suspension structure located in the suspension area 210. According to the following formula (I), the minimum sensing signal (a min ) of the MEMS device is positively correlated with the mass of the mass 130. Therefore, the MEMS device provided with the mass 130 in this embodiment can be applied to a wireless Bluetooth headset to assist the voice vibration of the microphone. Formula (I): where κ B is the Boltzmann constant; T is the absolute temperature; ω0 is the resonance frequency; m i is the mass of the sensor; Q is the quality factor.

[0057] Those of ordinary skill in the art should also understand that the MEMS device of the present invention and its forming method are not limited to the foregoing, but may have other aspects or variations. For example, although in the foregoing process, the MEMS device is formed on a bulk silicon substrate as an implementation aspect for illustration, its actual process is not limited thereto, and it can be alternatively operated on a silicon-on-insulator (SOI) substrate. Other embodiments or variations of the MEMS device of the present invention and its forming method will be described below. And for the sake of simplicity of description, the following description mainly details the differences of each embodiment, and the same parts will not be repeated. In addition, the same elements in each embodiment of the present invention are labeled with the same reference numerals for easy comparison between embodiments.

[0058] In another embodiment of the present invention, a microelectromechanical device and a method for forming the same are further disclosed. On the premise that the minimum sensing signal (a min ) of the microelectromechanical device is positively correlated with the mass of the mass block, and the mass of the mass block is related to the rigidity of the suspension structure in the suspension region 210, a mass block with more optimized (heavier) mass but not affecting the stiffness of the suspension structure is further provided. Please refer to Figures 4 to 7 . As shown, it is a schematic diagram showing the method for forming the microelectromechanical device in the second embodiment of the present invention. The forming method of this embodiment is generally similar to the foregoing embodiment in steps, and the similar parts will not be elaborated again. The main difference between this embodiment and the foregoing embodiment is that the mass block 330 of this embodiment is partially suspended above the interconnect structure 200.

[0059] As Figure 4 shown, 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 this embodiment are generally the same as those in the foregoing first embodiment, and will not be elaborated again. Then, a 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 holes 207, as Figure 4 shown. In one embodiment, the base material layer 331 includes, for example, materials such as silicon oxide or silicon dioxide, but is not limited thereto.

[0060] Then, as Figure 5 shown, at least one opening is formed in the base material layer 331 and the top dielectric layer 209, and the at least one opening is located within the suspension region 210. Preferably, the at least one opening is formed at a position adjacent to the through hole 207 on the suspension structure. In this embodiment, one opening is formed, and the opening may have an annular appearance when viewed from a top view (not shown), and may present two mutually separated holes 332 when viewed from a cross-section, as Figure 5 shown, but the setting manner and aspect of the opening are not limited thereto. That is to say, when viewed from a top-down perspective, the aforementioned two mutually separated holes 332 may be connected to each other, but are not limited thereto. In another embodiment, various numbers of openings may also be formed at positions adjacent to the through hole 207 according to actual process requirements. Then, a mass layer 333 is formed on the base material layer 331. The mass layer 333 is also formed within the suspension region 210, and further fills the aforementioned holes 332 to form protrusions 333a, so that the protrusions 333a can surround the outside of a part of the base material layer 331, as Figure 5As shown. The formation of the mass layer 333 may include the following steps. First, a mass material layer (not shown) is formed on the base material layer 331 such that the mass material layer entirely covers all surfaces of the base material layer 331, and then the mass material layer is patterned to form Figure 5 the mass layer 333 as shown. In one embodiment, the mass layer 333 includes any suitable material with a relatively high mass density, such as aluminum copper, copper, gold, platinum, molybdenum, or silicon, but is not limited thereto. 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 approximately 5 micrometers to 15 micrometers, preferably 10 micrometers, but not limited thereto. In addition, the thickness of the mass layer 333 can also be adjusted individually according to the thickness of the connection pads located on the surface of the interconnect structure 200.

[0061] As Figure 6 shown, 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, before forming the trench 103, a protective layer 350 is first formed on the interconnect structure 200 to cover the mass layer 333, the base material layer 331, and the interconnect structure 200, thereby protecting the components disposed therebelow. The protective layer 350 includes, for example, silicon oxide, silicon dioxide, or other materials having the same or similar etching selectivity as the material of the underlying base material layer 331. Then, a masking layer (not shown) is formed on the second surface 102 to define the position and size of the trench 103, and then an etching process, such as an anisotropic dry etching process, is performed from the back side of the substrate 100 through the masking layer to remove a certain degree of the substrate 100 until a portion of the underlying oxide layer 110 is exposed. In one embodiment, the masking layer has an opening, and the opening preferably corresponds to the suspension structure disposed in the suspension area 210, and the size of the opening is preferably equal to the predetermined size of the trench 103, such as approximately 100 micrometers to 150 micrometers, but is not limited thereto.

[0062] Thereby, the trench 103 is formed in the substrate 100 by using the oxide layer 110 as an etching stop layer, such that the trench 103 can extend between two opposite surfaces (the first surface 101 and the second surface 102) of the substrate 100 and has a depth equal to the thickness T1 of the substrate 100. In addition, the trench 103 can face the suspension structure within the suspension area 210 of the interconnect structure 200 disposed on the first surface 101, and the trench 103 has an opening 103a at the bottom surface adjacent to the suspension area 210, as Figure 6 shown.

[0063] After that, as Figure 7As shown, 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 suspended region 210 can be partially exposed and can communicate with the trench 103. It should be noted that during the other etching process, the sidewalls of the remaining oxide layer 110 can also be slightly removed to form an undercut portion 111 at the opening 103a adjacent to the trench 103. Then, the protective layer 350 and the base material layer 331 are removed, thereby releasing the suspended structure within the suspended region 210 of the interconnect structure 200. In this way, one end of the suspended structure (which can also be referred to as the free end F) is not connected to the substrate 100 and is in a suspended state, while the other end of the suspended structure (which can also be referred to as the anchor end A) remains connected to the substrate 100, so that when the MEMS device operates and causes the suspended structure to vibrate, more stress should be concentrated at the anchor end A of the suspended structure, and less stress will be concentrated at the free end F of the suspended structure.

[0064] In one embodiment, the protective layer 350 and the base material layer 331 can be optionally removed when removing the partially exposed oxide layer 110, but it is not limited thereto. In another embodiment, the protective layer 350 and the base material layer 331 can also be optionally removed additionally by another isotropic wet etching process. It should be noted that when removing the protective layer 350 and the base material layer 331, the protective 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. Thus, the base layer 331a as shown in Figure 7 can be formed. Thus, the base layer 331a and the mass layer 333 can jointly form the mass block 330 of this embodiment. The mass block 330 of this embodiment includes a bilayer structure, wherein the base layer 331a and the protrusion 333a surrounding the outside of the base layer 331a are disposed at the bottom layer of the bilayer structure, and the mass layer 333 disposed above the base layer 331a and the protrusion 333a is located at the top layer of the bilayer structure. It should be noted that only the bottom layer (the base layer 331a and the protrusion 333a) of the mass block 330 is directly disposed on the suspended structure of the suspended region 210 and is disposed at a position adjacent to the free end F of the suspended structure, while the top layer (the mass layer 333) of the mass block 330 can extend from the free end F of the suspended structure to the anchor end A, so that one end of the top layer can be suspended above the anchor end A, as shown in Figure 7 shown.

[0065] Thus, the MEMS device in the second embodiment of the present invention can be formed. In this embodiment, the MEMS device includes a suspension structure, a trench 103, and a mass 330 disposed in the suspension area 210 of the interconnect structure 200. It can also be used as a MEMS accelerator. When receiving acoustic waves or electrical signals, it can vibrate through the piezoelectric layer disposed in the suspension structure, and the mass 330 is used to adjust the suspension structure so that the suspension structure has a resonance frequency that can meet the required sensed audio range. It should be noted that the mass 330 in this embodiment includes a double-layer structure, which is composed of a bottom layer (base layer 331a and protrusion 333a) and a top layer (mass layer 333), so that the top layer can extend from the free end F to the anchor end A of the suspension structure, so that the mass layer 330 in this embodiment can have the advantages of a relatively large thickness T2, a relatively large size, and a relatively large mass. Among them, 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 described above, for example, about 5 μm to 15 μm, preferably 10 μm, but not limited thereto. In addition, only the bottom layer (base layer 331a and protrusion 333a) of the mass 330 in this embodiment is directly disposed on the suspension structure and is located in the area with less stress distribution in the suspension structure (i.e., the area near the free end F), while the top layer (mass layer 333) of the mass 330 can be disposed above the anchor end A in a suspended manner at one end and does not directly contact the stress concentration area of the suspension structure. Thus, the mass 330 with a relatively large thickness, a relatively large size, and a relatively large mass in this embodiment does not affect the stiffness of the suspension structure located in the suspension area 210, thereby providing more optimized sensing sensitivity. Therefore, the MEMS device of the present invention having the aforementioned mass 330 can be applied to wireless Bluetooth headsets to assist the voice vibration of the microphone.

[0066] Please refer to Figure 8 as shown, which is a schematic diagram showing the formation method of the MEMS device in the third embodiment of the present invention. The formation method of this embodiment is generally similar to that of the second embodiment described above, and the similar parts will not be described again. The main difference between this embodiment and the previous embodiment is that the mass layer 533 of the mass 530 is only located on the top layer of the double-layer structure and does not extend downward and surround the base layer 531 located at the bottom layer of the double-layer structure.

[0067] Specifically, the mass layer 533 of this embodiment is directly formed on, such as Figure 4On the shown base material layer 331. Then, similar to the process in the second foregoing embodiment, after forming the protective layer 350, continue to form the trench 103, and then remove the oxide layer 110, the protective layer 350, and the base material layer 331 through an isotropic wet etching process. It should be noted that when removing the base material layer in this embodiment through this isotropic wet etching process, it is necessary to further control etching conditions such as the etching rate and the etching time to form a base layer 531 as shown in Figure 8 such that the base layer 531 will only be formed in the region with less stress distribution (i.e., the region near the free end F), rather than causing all of the base material layer to be removed. In this case, the base layer 531 and the mass layer 533 can also jointly form the mass block 530 of this embodiment, and the mass block 530 is also disposed at a position adjacent to the free end F of the suspension structure, without affecting the stiffness of the suspension structure located within the suspension region 210.

[0068] Thus, the MEMS device in the third embodiment of the present invention can be formed. The MEMS device also includes a suspension structure, a trench 103, and a mass block 530 disposed within the suspension region 210 of the interconnect structure 200, and can also be used as a MEMS system accelerator. When receiving a sound wave or an electrical signal, it can vibrate through the piezoelectric layer disposed within the suspension structure, and adjust the suspension structure through the mass block 530 such that the suspension structure has a resonance frequency that can meet the required sensing audio range. It should be noted that the mass block 530 of this embodiment also has a relatively large size, a relatively large mass, and a relatively large thickness T2. For example, the thickness T2 of the mass block 530 is about 5 micrometers to 15 micrometers, but not limited thereto. Moreover, the mass block 530 with a relatively large thickness, a relatively large size, and a relatively large mass in this embodiment does not affect the stiffness of the suspension structure located within the suspension region 210, thereby providing more optimized sensing sensitivity. Therefore, the MEMS device of the present invention having the foregoing mass block 530 can be applied to a wireless Bluetooth headset to assist the voice vibration of the microphone.

[0069] Generally speaking, the present invention provides a detection mass block with a double-layer structure. The bottom layer of the mass block is directly disposed on the suspension structure located within the suspension area and in the area with less stress distribution on the suspension structure, while the top layer of the mass block is disposed on the bottom layer. Thus, one end of the top layer of the mass block is directly disposed on the bottom layer, and the other end of the top layer further extends and is suspended above the suspension structure without directly contacting the suspension structure located within the suspension area. Thereby, the present invention can fully expand the size, mass, thickness, etc. of the mass block on the premise of not affecting the rigidity of the suspension structure, which is beneficial to improving the sensing sensitivity of the microelectromechanical device. Therefore, the microelectromechanical device having the aforementioned mass block can be applied to a wireless Bluetooth headset to assist the voice vibration of the microphone. In addition, those of ordinary skill in the art should easily understand that although the mass block with a double-layer structure is described as an implementation mode in the foregoing embodiments of the present invention, the actual structure of the mass block is not limited thereto. In another embodiment, a mass block with a multi-layer structure can also be selected to be formed, which can also present a partially suspended state and be suspended on the stress concentration area of the suspension structure to avoid affecting the rigidity of the suspension structure while improving the sensing sensitivity of the microelectromechanical device.

[0070] The foregoing are only the preferred embodiments of the present invention, and all equivalent changes and modifications made according to the claims of the present invention shall fall within the protection scope of the present invention.

Claims

1. A microelectromechanical device, characterized in that, Comprising: a substrate having a first surface and a second surface opposite to the first surface; a trench disposed within 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 above the trench, the interconnect structure including a suspended region corresponding to the trench and a through hole in the suspended region, wherein a first end of the suspended region near the through hole is not connected to the substrate; and a mass block disposed on the interconnect structure, wherein the mass block is partially suspended above the interconnect structure.

2. The microelectromechanical device according to claim 1, wherein The mass block includes a base layer and a mass layer, the base layer being directly disposed on the interconnect structure, and the mass layer being disposed on the base layer.

3. The microelectromechanical device according to claim 2, wherein One end of the mass layer is located on the base layer, and the other end of the mass layer is suspended on the interconnect structure.

4. The microelectromechanical device according to claim 2, wherein The mass layer further includes a protrusion surrounding a sidewall of the base layer.

5. The microelectromechanical device according to claim 4, characterized in that, The protrusion directly contacts the interconnect structure.

6. The microelectromechanical device according to claim 2, characterized in that, A second end of the suspended region is connected to the substrate.

7. The microelectromechanical device according to claim 6, wherein, The base layer is disposed at a position adjacent to the first end of the suspended region.

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

9. The microelectromechanical device according to claim 1, wherein It further includes an oxide layer disposed between the interconnect structure and the substrate.

10. The microelectromechanical device according to claim 1, characterized in that, The thickness of the trench is the same as the thickness of the substrate.

11. The microelectromechanical device according to claim 1, wherein At least one end of the mass block is suspended above the interconnect structure.

12. A method for forming a microelectromechanical device, characterized in that, Comprising: providing a substrate having a first surface and a second surface opposite to the first surface; forming a trench within the substrate, the trench extending between the first surface and the second surface; forming an interconnect structure on the first surface of the substrate, the interconnect structure being above the trench, and the interconnect structure including a suspended region corresponding to the trench and a through hole in the suspended region, wherein a first end of the suspended region near the through hole is not connected to the substrate; and forming a mass block on the interconnect structure, wherein the mass block is partially suspended above the interconnect structure.

13. The method for forming the microelectromechanical device according to claim 12, wherein, The formation of the mass block is after the formation of the trench.

14. The method for forming a microelectromechanical device according to claim 12, wherein, The formation of the mass block further includes: forming a base layer on the interconnect structure; and forming a mass layer.

15. The method for forming a microelectromechanical device according to claim 14, wherein, It further includes: forming a base material layer on the interconnect structure; forming the mass layer on the base material layer before the formation of the trench; and after the formation of the trench, partially removing the base material layer to form the base layer.

16. The method for forming a microelectromechanical device according to claim 15, wherein, It further includes: forming the through hole on the base layer before the formation of the trench; and forming the mass layer, the mass layer including a protrusion disposed within the through hole.

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

18. The method for forming a microelectromechanical device as claimed in claim 12, wherein, It further includes: forming an oxide layer between the interconnect structure and the substrate; and after forming the trench, partially removing the oxide layer to communicate the trench and the interconnect structure.

19. The method for forming a microelectromechanical device according to claim 12, wherein, The formation of the trench includes: Removing the substrate from the second surface portion.

20. The method for forming a microelectromechanical device according to claim 12, wherein, At least one end of the mass block is suspended above the interconnect structure.

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