MEMS device and manufacturing method thereof

Abstract

The invention discloses an MEMS device and a manufacturing method thereof, and the manufacturing method comprises the steps: providing a substrate, the substrate comprises a substrate layer, a device layer and a pre-buried sacrificial layer located between the substrate layer and the device layer, the device layer is provided with a groove body to form an MEMS device structure, and the groove body penetrates through the device layer in the thickness direction; forming a sacrificial layer on the device layer, wherein the groove body on the device layer is filled with the sacrificial layer; forming a cap layer on the sacrificial layer, and forming a release hole in the cap layer; removing a part of the sacrificial layer and a part of the pre-buried sacrificial layer by using the release holes, forming a packaging cavity covering the MEMS device structure between the device layer and the cap layer, and enabling a resonant structure of the MEMS device structure to be in a suspended state relative to the substrate layer; and performing vacuum treatment on the packaging cavity, and sealing the release hole.

Description

Technical Field

[0001] This invention relates to the field of microelectromechanical systems (MEMS) technology, and more particularly to a method for manufacturing MEMS devices. Background Technology

[0002] The Q-factor of a MEMS (Micro-Electro-Mechanical Systems) resonator is one of the key parameters for evaluating its performance. A high Q-factor requires a high vacuum environment (e.g., a vacuum level below 1 Pa), which necessitates MEMS vacuum packaging. MEMS vacuum packaging can be divided into device-level vacuum packaging and wafer-level vacuum packaging. Device-level vacuum packaging has low packaging efficiency and results in a larger overall device size, making miniaturization difficult. Wafer-level packaging, on the other hand, encapsulates all devices on the entire wafer simultaneously, resulting in high packaging efficiency, smaller package size, and facilitating large-scale mass production.

[0003] Existing wafer-level vacuum packaging typically uses bonding for encapsulation. However, bonding requires the additional use of cap wafers and bonding rings for fixation and encapsulation, resulting in relatively high costs. Furthermore, sufficient bonding area needs to be maintained between the cap wafer and the device wafer to meet bonding strength and hermeticity requirements, leading to a larger overall size of the packaged device. At the same time, the bonding process has high requirements for the cleanliness and flatness of the wafer surface, making the process quite complex. Summary of the Invention

[0004] In view of this, the present invention provides a method for manufacturing MEMS devices that is low in cost, small in size, and relatively simple in process.

[0005] On one hand, this application provides a method for manufacturing a MEMS device, comprising:

[0006] A substrate is provided, the substrate including a substrate layer, a device layer and a pre-embedded sacrificial layer located between the substrate layer and the device layer, the device layer having a groove to form a MEMS device structure, the groove penetrating the device layer along the thickness direction;

[0007] A sacrificial layer is formed on the device layer, and the sacrificial layer fills the groove on the device layer;

[0008] A capping layer is formed on the sacrificial layer, and a release hole is provided on the capping layer;

[0009] By using the release hole to remove part of the sacrificial layer and part of the pre-embedded sacrificial layer, an encapsulation cavity covering the MEMS device structure is formed between the device layer and the capping layer, and the resonant structure of the MEMS device structure is suspended relative to the substrate layer.

[0010] The encapsulation cavity is subjected to vacuum treatment to seal the release hole.

[0011] In some embodiments, the vacuum treatment of the encapsulation cavity includes:

[0012] A getter is formed on the device layer;

[0013] When the sacrificial layer is released, the getter fixed on the device layer is exposed, and the getter is activated to absorb air in the encapsulation cavity, so that the MEMS device structure is in a vacuum environment.

[0014] In some embodiments, forming a getter on the device layer includes:

[0015] A metal adhesion layer is deposited on the device layer;

[0016] A getter film is deposited on the metal adhesion layer to form a gas-absorbing film;

[0017] An inert metal layer is deposited on the gas-absorbing film to obtain a gas-absorbing layer having a metal adhesion layer, a gas-absorbing film, and an inert metal layer;

[0018] The getter layer is patterned to obtain multiple getters spaced apart on the device layer.

[0019] In some embodiments, the vacuum treatment of the encapsulation cavity includes:

[0020] A getter is formed on the sacrificial layer;

[0021] When the sacrificial layer is released, the getter fixed on the cap layer is exposed, and the getter is activated to absorb air in the encapsulation cavity, so that the MEMS device structure is in a vacuum environment.

[0022] In some embodiments, forming the getter on the sacrificial layer includes:

[0023] An inert metal layer is deposited on the sacrificial layer;

[0024] A getter film is deposited on the inert metal layer to form a getter film;

[0025] A metal adhesion layer is deposited on the gas-absorbing film to obtain a gas-absorbing layer having an inert metal layer, a gas-absorbing film, and a metal adhesion layer;

[0026] The getter layer is patterned to obtain multiple getters spaced apart on the sacrificial layer.

[0027] In some embodiments, including:

[0028] Through-holes are formed by etching in the sacrificial layer, and the through-holes penetrate the sacrificial layer along the thickness direction;

[0029] The capping layer is deposited on the sacrificial layer having the via, the capping layer including a capping body located on the side of the sacrificial layer away from the device layer, and a support post located within the via.

[0030] In some embodiments, the inner diameter of the top of the via is greater than the inner diameter of the bottom, so that the inner wall of the via extends inward from top to bottom, and the angle between the inner wall of the via and the bottom wall of the sacrificial layer near the device layer is less than or equal to 60°.

[0031] In some embodiments, including:

[0032] The sacrificial layer is graphically processed to define the position and size of the encapsulation cavity.

[0033] In some embodiments, after forming the capping layer on the sacrificial layer, the method further includes:

[0034] A contact hole is provided on the cap layer, and the contact hole penetrates the cap body and the support column along the thickness direction;

[0035] A conductive layer is provided inside the contact hole and on the side of the cap body away from the device layer;

[0036] A sealing film is formed on the cap body, the sealing film sealing the release hole and exposing the conductive layer.

[0037] In some embodiments, it also includes:

[0038] A passivation layer is deposited on the sealing film, the passivation layer exposing the conductive layer;

[0039] A reinforcing layer is formed by coating the surface of the passivation layer, and the thickness of the reinforcing layer is greater than the thickness of the passivation layer.

[0040] In some embodiments, removing a portion of the sacrificial layer and a portion of the pre-embedded sacrificial layer using the release hole includes:

[0041] An etchant is injected through the release hole to remove the sacrificial layer corresponding to the location of the packaging cavity, the sacrificial layer located in the groove, and the pre-embedded sacrificial layer located below the MEMS device.

[0042] In some embodiments, forming a sacrificial layer on the device layer includes:

[0043] A first sacrificial layer is formed on the device layer;

[0044] A recess is provided on the first sacrificial layer, and the recess extends to the surface of the device layer;

[0045] A second sacrificial layer is formed on the device layer at a position corresponding to the recess, and the thickness of the second sacrificial layer is less than the thickness of the first sacrificial layer.

[0046] In some embodiments, the cap layer includes a cap body and a protrusion located on one side of the cap body, the protrusion being located within the recess and extending to connect with the second sacrificial layer, the release hole penetrating the cap body and the protrusion; removing a portion of the sacrificial layer and a portion of the pre-embedded sacrificial layer using the release hole includes:

[0047] An etchant is injected through the release hole to remove the second sacrificial layer located below the protrusion by etching, thereby forming a release channel between the protrusion and the device layer;

[0048] The corrosive agent removes a portion of the first sacrificial layer and a portion of the pre-embedded sacrificial layer located laterally outside the protrusion through the release channel.

[0049] In some embodiments, sealing the release orifice includes:

[0050] A sealing film is formed on the cap layer to cover and fill the release hole; wherein the sealing film includes a main body portion on the cap layer, a first sealing portion filling the release hole, and a second sealing portion located between the protrusion and the device layer, the second sealing portion sealing the release channel, and the second sealing portion being disposed at intervals on the outside of the MEMS device structure.

[0051] On the other hand, this application also provides a MEMS device, which is manufactured using the manufacturing method described above.

[0052] This invention provides a method for manufacturing a MEMS device. First, a sacrificial layer is formed on the device layer. Then, a capping layer is formed on the sacrificial layer. A release hole on the capping layer is used to remove the corresponding area of ​​the sacrificial layer and the pre-embedded sacrificial layer, thereby forming an encapsulation cavity inside the MEMS device. This allows the resonant structure of the MEMS device to be suspended. The encapsulation cavity is then vacuum-treated, and the release hole is sealed, placing the MEMS device structure in a vacuum and sealed environment to prevent external air from affecting its operation. Furthermore, the manufacturing process of the MEMS device eliminates the need for additional bonding rings and corresponding fixing operations, which helps reduce production costs and manufacturing difficulty. It also reduces the area on the device layer used for connection with the capping layer, thus reducing the overall volume of the MEMS device. Ultimately, this method achieves a manufacturing method that integrates low cost, small size, and simple process. Attached Figure Description

[0053] Figure 1 A flowchart illustrating a method for manufacturing a MEMS device according to a first embodiment of the present invention;

[0054] Figure 2 This is a schematic diagram of the structure of the MEMS device provided in the first embodiment of the present invention;

[0055] Figure 3 for Figure 2 A schematic diagram of the substrate shown;

[0056] Figure 4 for Figure 3 The diagram shows a substrate forming a groove, which is a structural schematic.

[0057] Figure 5 for Figure 4 A schematic diagram of the structure when a getter is formed on the device layer shown in the figure;

[0058] Figure 6 for Figure 5 A schematic diagram of the structure when a sacrificial layer is formed on the device layer shown in the figure;

[0059] Figure 7 for Figure 6 A schematic diagram of the structure when a capping layer is formed on the sacrificial layer shown in the figure;

[0060] Figure 8 for Figure 7 A schematic diagram of the structure in which the cap layer forms the release hole and contact hole;

[0061] Figure 9 for Figure 8 A schematic diagram of the structure when a conductive layer is formed on the capping layer shown in the figure;

[0062] Figure 10 for Figure 9A schematic diagram of the structure when the sacrificial layer and the embedded sacrificial layer are removed to form the encapsulation cavity;

[0063] Figure 11 for Figure 10 A schematic diagram of the structure when a sealing film is formed on the cap layer shown in the figure;

[0064] Figure 12 This is a schematic diagram of the structure when a passivation layer is formed on the sealing film according to the second embodiment of the present invention;

[0065] Figure 13 for Figure 12 A schematic diagram of the structure when a reinforcing layer is formed on the passivation layer shown in the figure;

[0066] Figure 14 This is a schematic diagram of the structure when a getter is formed on the sacrificial layer according to the third embodiment of the present invention;

[0067] Figure 15 This is a schematic diagram of the structure of a MEMS device provided in the third embodiment of the present invention;

[0068] Figure 16 This is a schematic diagram of the structure when a first sacrificial layer and a second sacrificial layer are formed on a device layer according to the fourth embodiment of the present invention;

[0069] Figure 17 for Figure 16 A schematic diagram of the structure when a capping layer is formed on the second sacrificial layer shown in the figure;

[0070] Figure 18 for Figure 17 The diagram shows the structure when the first sacrificial layer, the second sacrificial layer, and the pre-embedded sacrificial layer are removed to form the encapsulation cavity.

[0071] Figure 19 for Figure 18 The diagram shows a structural schematic of a sealing film being formed on the cap layer. Detailed Implementation

[0072] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0073] It should be noted that all directional indications (such as up, down, left, right, front, back, inside, outside, top, bottom, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship between the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0074] It should also be noted that when a component is referred to as "fixed to" or "set on" another component, the component may be directly on the other component or there may be an intervening component present. When a component is referred to as "connected to" another component, it may be directly connected to the other component or there may be an intervening component present.

[0075] Please see Figure 1 and Figure 2 The first embodiment of the present invention provides a method for manufacturing a MEMS device, comprising:

[0076] S101: Provide a substrate, the substrate including a substrate layer, a device layer and a pre-embedded sacrificial layer located between the substrate layer and the device layer, the device layer having a groove to form a MEMS device structure, the groove penetrating the device layer along the thickness direction;

[0077] The substrate 11 has a "sandwich" structure, including a substrate layer 13, a pre-embedded sacrificial layer 15, and a device layer 17 stacked sequentially. The substrate layer 13 supports the device layer 17, and the pre-embedded sacrificial layer 15 separates the substrate layer 13 and the device layer 17 and fixes them together. The pre-embedded sacrificial layer 15 can also serve as a sacrificial layer, and a portion of it can be removed during subsequent processing to allow a corresponding portion of the device layer 17 to be suspended relative to the substrate layer 13. A groove 19 is formed on the device layer 17, extending through it along its thickness direction. Specifically, the groove 19 extends from the surface of the device layer 17 away from the substrate layer 13 to the surface of the pre-embedded sacrificial layer 15. The device layer 17 forms a MEMS device structure 21 through the groove 19. This MEMS device structure 21 includes a resonant structure and a fixed structure (e.g., an anchor point structure). The resonant structure can resonate relative to the fixed structure and the substrate layer 13.

[0078] S102: A sacrificial layer is formed on the device layer, and the sacrificial layer fills the groove on the device layer;

[0079] The sacrificial layer 23 is used to temporarily support the subsequently formed capping layer 25 and can be etched away in a subsequent release process. The sacrificial layer 23 is partially located on the surface of the device layer 17 away from the substrate layer 13, partially located in the trench 19 on the device layer 17, and extends from the top of the trench 19 to the surface of the embedded sacrificial layer 15 to fill the trench 19.

[0080] S103: A capping layer is formed on the sacrificial layer, and a release hole is provided on the capping layer;

[0081] The sacrificial layer 23 is located between the cap layer 25 and the device layer 17 to separate the cap layer 25 wholly or partially from the device layer 17. A release hole 27 extends through the cap layer 25 along its thickness direction to the surface of the sacrificial layer 23, for use in subsequent processes to remove the corresponding portion of the sacrificial layer 23 and the embedded sacrificial layer 15. In an optional example, the release hole 27 is located above the MEMS device structure 21.

[0082] S104: Using the release hole, a portion of the sacrificial layer and a portion of the pre-embedded sacrificial layer are removed to form an encapsulation cavity covering the MEMS device structure between the device layer and the capping layer, and the resonant structure of the MEMS device structure is suspended relative to the substrate layer.

[0083] By injecting etchant into the release hole 27, the etchant contacts the sacrificial layer 23 located below it, thereby etching away a portion of the sacrificial layer 23 located above the device layer 17 to form an encapsulation cavity 29 between the device layer 17 and the cap layer 25. The encapsulation cavity 29 at least covers the resonant structure of the MEMS device structure 21 to avoid affecting the resonance of the resonant structure. After removing the portion of the sacrificial layer 23 above the device layer 17, the etchant continues to etch away the sacrificial layer 23 and a portion of the pre-buried sacrificial layer 15 within the tank 19, thereby making the resonant structure of the resonant device structure 21 suspended relative to the substrate layer 13.

[0084] The sacrificial layer 23 is not etched away at least in the area close to the periphery of the device layer 17 to secure the cap layer 25 and the device layer 17, while also creating a sealing effect at the periphery. Similarly, the embedded sacrificial layer 15 is not etched away at least in the area close to the periphery of the device layer 17 to secure the substrate layer 13 and the device layer 17, while also creating a sealing effect at the periphery.

[0085] The specific type of etchant is not limited and can be selected according to the material to be etched away. It can be a corrosive liquid or a corrosive gas. Preferably, the etchant is a corrosive gas to avoid adhesion of the structure caused by liquid corrosion. When the material of the sacrificial layer 23 is the same as that of the embedded sacrificial layer 15, the same etchant can be used to remove both sacrificial layer 23 and embedded sacrificial layer 15. When they are different materials, different etchants can be selected to remove sacrificial layer 23 and embedded sacrificial layer 15 sequentially. When the material to be etched is SiO2, gaseous HF gas can be selected as the etchant; when the material to be etched is PI, O2 gas can be selected as the etchant.

[0086] S105: Vacuum treatment is performed on the encapsulation cavity to seal the release hole.

[0087] The packaging cavity is vacuum-treated to remove the air inside the packaging cavity, and then the release hole is sealed, so that the MEMS device structure 21 is in a vacuum and sealed environment, avoiding the influence of air on the operation of the MEMS device structure, thereby improving the performance of the fabricated MEMS device.

[0088] During the manufacturing process of MEMS devices using the above-described manufacturing method, the cap layer 25, sacrificial layer 23, and device layer 17 are automatically fixed together, and then vacuum and sealing treatment is performed. There is no need to introduce additional bonding rings or other devices for fixation, which helps to reduce production costs and manufacturing difficulty. At the same time, it can also reduce the area of ​​the device layer 17 used for connection with the cap layer 25, which helps to reduce the overall volume of the MEMS device. This achieves a manufacturing method that integrates low cost, small size, and simple process.

[0089] Please see Figure 3 and Figure 4 In one embodiment, a substrate is provided, comprising:

[0090] Provide a substrate layer;

[0091] The substrate layer 13 is a silicon wafer, which is used to support the device layer 17 and the cap layer 25 located above it.

[0092] A pre-embedded sacrificial layer is deposited on the substrate layer;

[0093] The pre-embedded sacrificial layer 15 is made of materials that can be etched away, such as SiO2, Si3N4 or PI (Polyimide), and its thickness is between 0.5 and 10 μm.

[0094] Fabricate a device layer on a pre-embedded sacrificial layer;

[0095] Device layer 17 is made of silicon and can be fabricated using processes such as CVD (Chemical Vapor Deposition), epitaxy, sputtering, or bonding, with a thickness between 1 and 50 μm. Furthermore, device layer 17 can be p-type or n-type doped during fabrication, i.e., specific impurities can be added to make the resistivity of device layer 17 ≤ 1 ohm·cm.

[0096] Part of the device layer is removed through patterning to form a groove on the device layer.

[0097] The patterning process includes photolithography and dry etching. Photolithography is used to define the parts that need to be removed, while dry etching removes the corresponding parts and stops at the surface of the pre-embedded sacrificial layer 15, thereby forming the groove 19 and then forming the MEMS device structure 21.

[0098] In other embodiments, a substrate 11 having a substrate layer 13, a pre-embedded sacrificial layer 15, and a device layer 17 can be used directly, without the need to prepare the substrate layer 13, the pre-embedded sacrificial layer 15, and the device layer 17 sequentially during the production process.

[0099] Please see Figure 5 In one embodiment, the vacuum treatment of the encapsulation cavity includes:

[0100] A getter is formed on the device layer;

[0101] The getter 31 is located inside the encapsulation cavity 29 and can be used to absorb the gas inside the encapsulation cavity 29, thereby creating a vacuum effect in the encapsulation cavity 29. Optionally, the getter 31 can be made of metallic Ti, metallic Zr, or an alloy of Ti, Zr and other elements.

[0102] When the sacrificial layer is released, the getter fixed on the device layer is exposed, and the getter is activated to absorb air in the encapsulation cavity, so that the MEMS device structure is in a vacuum environment.

[0103] Once activated, the getter 31 can absorb the air remaining in the packaging cavity 29 during the production process, as well as the gas released by the MEMS device materials during use, in order to maintain the long-term vacuum stability inside the packaging cavity 29.

[0104] In one embodiment, forming a getter on the device layer includes:

[0105] A metal adhesion layer is deposited on the device layer;

[0106] The metal adhesion layer can improve the bonding force between the getter 31 and the device layer 17, and enhance the stability of the getter 31 on the device layer 17.

[0107] A getter film is deposited on the metal adhesion layer to form a gas-absorbing film;

[0108] The gas-absorbing membrane can absorb gases and can be made of metallic Ti, metallic Zr, or an alloy of Ti, Zr and other elements.

[0109] An inert metal layer is deposited on the gas-absorbing film to obtain a gas-absorbing layer having a metal adhesion layer, a gas-absorbing film, and an inert metal layer;

[0110] An inert metal layer can cover the getter film, preventing it from contacting air and thus preventing the getter film from absorbing large amounts of air during processing. This would reduce its ability to absorb gas later, affecting its function of maintaining the vacuum of the encapsulation cavity. When a getter is needed to absorb gas, it is activated to allow the getter film to contact air. Optionally, the inert metal layer can be made of inert metals such as Pt or Au.

[0111] The getter layer is patterned to obtain multiple getters spaced apart on the device layer.

[0112] By patterning, at least the getter layer on the resonant structure of device layer 17 is removed to prevent it from affecting the resonance of the resonant structure, thereby forming multiple spaced getters 31 on the non-resonant structure of device layer 17.

[0113] Patterning the getter layer can be done using the liftoff method in semiconductor processes, or by photolithography and etching.

[0114] The getter 31 can be activated by baking it in a vacuum environment to heat it and thus activate it, or by irradiating the surface of the getter with a light source such as visible light or infrared light to activate it.

[0115] Please see Figure 6 and Figure 7 In one embodiment, it further includes:

[0116] Through-holes are formed by etching in the sacrificial layer, and the through-holes penetrate the sacrificial layer along the thickness direction;

[0117] Optionally, the number of through holes 33 on the sacrificial layer 23 is multiple, and the multiple through holes 33 are arranged at intervals.

[0118] The capping layer is deposited on the sacrificial layer having the via, such that the capping layer includes a capping body located on the side of the sacrificial layer away from the device layer, and a support post located within the via.

[0119] Since the sacrificial layer 23 has through holes 33, during the deposition of the capping layer 25, part of the material forming the capping layer 25 fills the through holes 33 on the sacrificial layer 23 and part is located on the surface of the device layer 17 away from the substrate layer 13, so that the capping layer 25 includes two parts: the capping body 35 and the support pillar 37.

[0120] After the sacrificial layer 23 is removed by corrosion to form the encapsulation cavity 29, the part of the cap body 35 opposite to the encapsulation cavity 29 is in a suspended state. The support column 37 is located inside the encapsulation cavity 29 and can support the suspended part, reduce the area of ​​the suspended part of the cap body 35, enhance the pressure bearing capacity of the cap body 35, reduce the thickness requirement of the cap body 35, so that it can withstand greater pressure with a thinner thickness, and reduce the risk of the cap body 35 being damaged under external pressure during subsequent processing.

[0121] Optionally, the sacrificial layer 23 can be prepared on the device layer 17 by a deposition process or a spin coating process. The deposition process can be CVD (Chemical Vapor Deposition) or PVD (Physical Vapor Deposition). The material for preparing the sacrificial layer 23 can be SiO2, Si3N4 or PI (Polyimide). In an optional example, the thickness of the portion of the sacrificial layer 23 located on the surface of the device layer 17 is 0.5 to 10 μm.

[0122] The capping layer 25 can be grown on the sacrificial layer 23 by at least one of the following processes: room temperature sputtering, low-temperature PECVD (Plasma-Enhanced Chemical Vapor Deposition), or electroplating, and the thickness of the capping layer 25 is between 1 and 50 μm. When using room temperature sputtering or low-temperature PECVD, the material used can be a dielectric material such as Si, Si3N4, or Al2O3. When using electroplating, the material used can be a metallic material such as Al or Ni. The capping layer 25 can be a single-layer structure, that is, the capping layer 25 can be a dielectric material layer or a metallic material layer, or it can be a multi-layer structure, such as a dielectric material layer + a metallic material layer, or a metallic material layer + a dielectric material layer, or a dielectric material layer + a metallic material layer + a dielectric material layer.

[0123] In one embodiment, the inner diameter of the top of the through hole 33 is larger than the inner diameter of the bottom of the through hole 33, causing the inner wall of the through hole 33 to extend inward from top to bottom. The support column 37 of the cap layer 25 fills the through hole 33, so the shape of the support column 37 is adapted to the shape of the through hole 33. The side of the support column 37 is inclined relative to the cap body 35, making the support column 37 an inverted frustum structure, such as an inverted frustum structure. When the cap body 35 is deformed under pressure, the point where the cap body 35 meets the edge of the support column 37 is the point of maximum stress. The inverted frustum structure of the support column 37 allows the stress at the point of maximum stress to be dispersed along the inclined surface of the support column 37, which has the effect of dispersing stress and avoiding the risk of damage due to excessive stress at the point of maximum stress.

[0124] The angle β between the inner wall of the through hole 33 and the bottom wall of the sacrificial layer 23 near the device layer 17 is less than or equal to 60°, that is, the angle between the side of the support pillar 37 and the surface of the device layer 17 is less than or equal to 60°, to avoid the problem of poor stress dispersion effect caused by an excessively large angle. Preferably, the angle β is in the range of 30° to 60°.

[0125] In some embodiments, it also includes:

[0126] The sacrificial layer is graphically processed to define the position and size of the encapsulation cavity.

[0127] By patterning the sacrificial layer 23, it is divided into parts that need to be removed and parts that do not need to be removed. The space where the parts to be removed are located forms the space for the package cavity 29. By controlling the position and size of the parts to be removed, the position and size of the package cavity 29 can be determined. The parts that do not need to be removed can be used to fix the device layer 17 and the cap layer 25, and seal the package cavity 29. Optionally, the patterning process can be performed using photolithography and dry etching.

[0128] Please see Figure 2 as well as Figures 8 to 11 In some embodiments, after forming the capping layer on the sacrificial layer, the process further includes:

[0129] A contact hole is provided on the cap layer, and the contact hole penetrates the cap body and the support column along the thickness direction;

[0130] A longitudinally extending contact hole 39 is formed on the surface of the cap layer 25 by photolithography and dry etching processes. The contact hole 39 penetrates the cap body 35 and the support post 37 along the thickness direction, and the support post 37 contacts the device layer 17, thereby extending the conductive hole to the surface of the device layer 17.

[0131] A conductive layer is provided inside the contact hole and on the side of the cap body away from the device layer;

[0132] A conductive layer 41 is formed and patterned within the contact hole 39 and on the surface of the cap body 35. The conductive layer 41 within the contact hole 39 is electrically connected to the device layer 17, and the conductive layer 41 on the surface of the cap body 35 can be used to electrically connect to external devices, thereby leading out electrical signals from the device layer 17. The conductive layer 41 can be a wire formed of metals such as Al, Au, or Ti.

[0133] A sealing film is formed on the cap body, the sealing film sealing the release hole and exposing the conductive layer.

[0134] After vacuum processing, a sealing film 43 is deposited on the cap body 35. The sealing film 43 covers the cap body 35 and the conductive layer 41 on the cap body 35, and fills the contact hole 39 and the release hole 27 to achieve a sealing effect. Then, the sealing film 43 is patterned, and part of the sealing film 43 is etched away by photolithography and etching processes to expose the conductive layer 41 for subsequent wire bonding and electrical connection with external devices.

[0135] Understandably, the release hole 27 and the contact hole 39 can be formed in the same step, that is, the release hole 27 and the contact hole 39 are formed longitudinally by photolithography and dry etching on the surface of the cap layer 25. The release hole 27 extends to the surface of the sacrificial layer 23 and is located above the MEMS device structure.

[0136] The shape of the release hole 27 is not limited; it can be a circular hole or a rectangular hole, etc. The diameter of the release hole 27 is less than or equal to 0.5 μm, which facilitates subsequent sealing and reduces the risk of sealing film material dripping onto the MEMS device structure 21 through the release hole 27. It also reduces the impact on the overall strength of the cap body 35.

[0137] Please see Figure 10 In some embodiments, removing a portion of the sacrificial layer and a portion of the pre-embedded sacrificial layer using the release hole includes:

[0138] An etchant is injected through the release hole to remove the sacrificial layer corresponding to the location of the packaging cavity, the sacrificial layer located in the groove, and the pre-embedded sacrificial layer located below the MEMS device.

[0139] The etchant enters the MEMS device through the release hole 27, first contacting the sacrificial layer 23 located below the release hole 27, and etches away part of the sacrificial layer 23 located above the device layer 17 to form an encapsulation cavity 29 between the device layer 17 and the cap layer 25, exposing the getter 31 on the device layer 17. Subsequently, the etchant continues to etch away the sacrificial layer 23 in the tank 19, and then contacts the pre-embedded sacrificial layer 15 through the tank 19, at least etching away part of the pre-embedded sacrificial layer 15 located below the resonant structure, so that the resonant structure is in a suspended state.

[0140] After the release is complete, i.e., after the corresponding sacrificial layer 23 and the pre-embedded sacrificial layer 15 are etched away, before depositing the sealing film 43, it is first baked in a vacuum environment to activate the getter 31 and absorb the gas in the encapsulation cavity 29. Then, the sealing film 43 is deposited on the cap layer 25 through a high-vacuum process such as sputtering or evaporation to form the sealing film 43. The sealing film 43 is used to seal the release hole 27, so that the resonant structure is in a sealed space and isolated from the outside world. Preferably, the sealing film 43 is formed by an evaporation process, which has a lower process vacuum degree.

[0141] In an optional example, the thickness of the sealing film 43 is 1–10 μm, and the material used can be a dielectric material such as Si, Si3N4, or Al2O3, or a metallic material such as Al, Ge, or ZnS, or a stack of films made of multiple materials. When the sealing film 43 is made of a dielectric material such as Si3N4 or Al2O3, it allows visible light to pass through; when the sealing film 43 is made of a metallic material such as Ge or ZnS, it allows infrared light to pass through, making it suitable for optical MEMS devices.

[0142] Second Embodiment

[0143] The mechanical strength of the MEMS device fabricated by the method of the first embodiment mainly relies on the mechanical strength of the capping layer and the sealing film. However, due to process limitations, the thickness of the capping layer and the sealing film cannot be too thick, thus limiting the strength. This embodiment proposes to additionally set a passivation layer and a reinforcement layer to further improve the mechanical strength of the MEMS device and meet the application requirements for better strength.

[0144] Please see Figure 12 and Figure 13 In this embodiment, the preparation method further includes:

[0145] A passivation layer is deposited on the sealing film, the passivation layer exposing the conductive layer;

[0146] By forming a passivation layer 45 on the sealing film 43, the passivation layer 45 can not only improve the overall mechanical strength of the product, but also protect the sealing film 43, isolate it from external oxygen and water corrosion, and improve the reliability of the product.

[0147] The passivation layer 45 can be deposited and grown on the surface of the sealing film 43 by processes such as sputtering or CVD, and patterned by photolithography and etching processes to expose the conductive layer 41. Optionally, the passivation layer 45 can be made of materials such as Si3N4 or SiO2, and the thickness is 0.5 to 10 μm.

[0148] A reinforcing layer is formed by coating the surface of the passivation layer, and the thickness of the reinforcing layer is greater than the thickness of the passivation layer.

[0149] The reinforcing layer 47 can further improve the mechanical strength of the product to enhance its pressure resistance.

[0150] The reinforcing layer 47 can be made of organic polymer materials with low Young's modulus such as PI and SU8 (epoxy negative photoresist), and its thickness is greater than or equal to 3μm.

[0151] Third Embodiment

[0152] In the MEMS device fabricated by the method of the first embodiment, the getter is located on the device layer. However, the device layer needs to form a resonant structure for resonance, and the getter needs to avoid the resonant structure. Therefore, the area on the device layer that can be used to place the getter is small, which limits the size and quantity of the getter.

[0153] Please see Figure 14 and Figure 15 In this embodiment, the vacuum treatment of the packaging cavity includes:

[0154] A getter is formed on the sacrificial layer;

[0155] When the sacrificial layer is released, the getter fixed on the cap layer is exposed, and the getter is activated to absorb air in the encapsulation cavity, so that the MEMS device structure is in a vacuum environment.

[0156] By first forming a sacrificial layer 23 on device layer 17, then forming a getter 31 on the sacrificial layer 23, and finally forming a capping layer 25 on the sacrificial layer 23, the getter 31 is located between the sacrificial layer 23 and the capping layer 25. After etching away the sacrificial layer 23, the getter 31 is fixed to the capping layer 25, creating an inverted mounting effect. Fixing the getter 31 to the capping layer 25 is not affected by the resonant structure; it only needs to avoid the location of the release hole 27, allowing for more getter to be placed within the packaging cavity 29.

[0157] In some embodiments, forming the getter on the sacrificial layer includes:

[0158] An inert metal layer is deposited on the sacrificial layer;

[0159] A getter film is deposited on the inert metal layer to form a getter film;

[0160] A metal adhesion layer is deposited on the gas-absorbing film to obtain a gas-absorbing layer having an inert metal layer, a gas-absorbing film, and a metal adhesion layer;

[0161] The getter layer is patterned to obtain multiple getters spaced apart on the sacrificial layer.

[0162] The metal adhesion layer can enhance the bonding force between the getter 31 and the capping layer 25, and enhance the stability of the getter 31 on the capping layer 25, while the inert metal layer can prevent the getter film from absorbing a large amount of air during processing.

[0163] In other embodiments, to further increase the amount of getter 31, getter 31 can be provided on both device layer 17 and cap layer 25. That is, during the manufacturing process, getter 31 can be deposited on device layer 17 first, then sacrificial layer 23 can be formed, and getter 31 can be deposited on sacrificial layer 23. After removing sacrificial layer 23 using release holes to form encapsulation cavity 29, part of getter 31 is fixed on device layer 17 and part of getter 31 is fixed on cap layer 25.

[0164] Fourth embodiment

[0165] In the first embodiment of the MEMS device, the release hole is formed by photolithography and etching processes. The smaller the diameter of the release hole, the easier the sealing and the better the sealing effect. However, the size of the release hole is defined by the photolithography process; the smaller the size, the greater the challenge to optical processes and corresponding equipment. Furthermore, since the release hole is located above the MEMS device structure, there is a risk that sealing film material may drip onto the MEMS device structure through the release hole during the sealing process, affecting its performance. To address this issue, this embodiment proposes a scheme to add a lateral release channel for the release operation.

[0166] Please see Figures 16 to 19 In this embodiment, forming a sacrificial layer on the device layer includes:

[0167] A first sacrificial layer is formed on the device layer;

[0168] A recess is provided on the first sacrificial layer, and the recess extends to the surface of the device layer;

[0169] Before defining the position and size of the packaging cavity 29, a recess 51 is formed on the first sacrificial layer 49 by photolithography and etching. The recess 51 extends from the upper surface to the lower surface of the first sacrificial layer 49, that is, the recess 51 extends to the surface of the device layer 17.

[0170] A second sacrificial layer is formed on the device layer at a position corresponding to the recess, and the thickness of the second sacrificial layer is less than the thickness of the first sacrificial layer.

[0171] After the cap layer 25 is formed on the second sacrificial layer 53, the cap layer 25 includes a cap body 35 and a protrusion 55. The cap body 35 is located on the side of the first sacrificial layer 49 away from the device layer 17, and the protrusion 55 is located in the recess 51 and extends to the second sacrificial layer 53. Since the second sacrificial layer 53 is provided in the recess 51, the thickness of the protrusion 55 on the cap layer 25 is less than that of the recess 51. The bottom end of the protrusion 55 is spaced at a certain distance from the device layer 17, that is, the distance between the two is the thickness of the second sacrificial layer 53.

[0172] Both the first sacrificial layer 49 and the second sacrificial layer 53 can be made of materials such as SiO2, Si3N4 or PI, and can be prepared by CVD, PVD or spin coating.

[0173] After the cap layer 25 is prepared, a release hole 27 is formed on the cap layer 25 at the position corresponding to the protrusion 55 by photolithography and etching process. The etching stops at the second sacrificial layer 53, so that the release hole 27 penetrates the cap body 35 and the protrusion 55.

[0174] In an alternative example, both the first sacrificial layer 49 and the second sacrificial layer 53 are prepared by a deposition process, and the second sacrificial layer 53 is also present on the side of the first sacrificial layer 49 away from the device layer 17. The capping layer 25 is prepared by deposition on the second sacrificial layer 53.

[0175] In some embodiments, removing a portion of the sacrificial layer and a portion of the pre-embedded sacrificial layer using the release hole includes:

[0176] An etchant is injected through the release hole to remove the second sacrificial layer located below the protrusion by etching, thereby forming a release channel between the protrusion and the device layer;

[0177] The corrosive agent removes a portion of the first sacrificial layer and a portion of the pre-embedded sacrificial layer located laterally outside the protrusion through the release channel.

[0178] After forming a release hole 27 on the cap layer 25, an etchant is injected through the release hole 27. The etchant first contacts the second sacrificial layer 53 below the release hole 27, etches away the second sacrificial layer 53 at that location, and then diffuses outwards, eventually removing the second sacrificial layer 53 in the entire recessed portion 51. This forms a release channel 57 between the protrusion 55 and the device layer 17. The release channel 57 extends laterally, and the etchant diffuses laterally outwards through the release channel 57, eventually removing the sacrificial layer and the pre-embedded sacrificial layer at the corresponding location, so that the resonant structure of the MEMS device structure is in a suspended state.

[0179] The size of the release channel 57 depends on the thickness of the second sacrificial layer 53, which is prepared by a deposition process. Its thickness control is relatively simple, which can reduce the difficulty of controlling the size of the release channel 57 during the preparation process.

[0180] In some embodiments, sealing the release orifice includes:

[0181] A sealing film is formed on the cap layer to cover and fill the release hole; wherein the sealing film includes a main body portion on the cap layer, a first sealing portion filling the release hole, and a second sealing portion located between the protrusion and the device layer, the second sealing portion sealing the release channel, and the second sealing portion being disposed at intervals on the outside of the MEMS device structure.

[0182] The main body 58 of the sealing film 43 is located above the cap layer 25. The first sealing part 59 seals the release hole 27, and the second sealing part 61 seals the release channel 57. Moreover, both the release hole 27 and the release channel 57 are located on the lateral outer side of the MEMS device structure 21, so that the first sealing part 59 and the second sealing part 61 are both located on the lateral outer side of the MEMS device structure 21. Therefore, when preparing the sealing film 43 on the cap layer 25, there is no need to worry about the sealing film material dripping onto the MEMS device structure 21 and affecting its working performance.

[0183] In this embodiment, the structure used for the release process consists of two parts: a release hole 27 and a release channel 57. The function of the release hole 27 is to expose the release channel 57. Its size requirement is relatively small. Moreover, the release hole 27 and the release channel 57 are located on the outside of the MEMS device structure 21. There is no need to consider the problem of sealing film material dripping onto the MEMS device structure 21 due to the size of the release hole 27. At the same time, the size of the release channel 57 is related to the thickness of the second sacrificial layer 53. The second sacrificial layer 53 is made by a deposition process, and the thickness control is relatively simple, which greatly reduces the manufacturing difficulty.

[0184] Please see Figure 2 and Figure 7The present invention also provides a MEMS device, such as a MEMS resonator, which includes a substrate 11, a capping layer 25 located above the substrate, and a sacrificial layer 23 connecting the substrate 11 and the capping layer 25. The substrate 11 has a "sandwich" structure, including a substrate layer 13, a pre-embedded sacrificial layer 15, and a device layer 17 from bottom to top. The pre-embedded sacrificial layer 15 connects the substrate layer 13 and the device layer 17 and separates them by a certain distance. The device layer 17 includes a MEMS device structure 21, the resonant structure of which is suspended relative to the substrate layer 13. The sacrificial layer 23 is connected between the periphery of the capping layer 25 and the periphery of the device layer 17. The capping layer 25 is provided with an encapsulation cavity 29, which at least covers the resonant structure.

[0185] The cap layer 25 includes a cap body 35 and a support post 37 located on one side of the cap body 35. The support post 37 is located inside the packaging cavity 29 and is connected between the non-resonant structural region of the device layer 17 and the cap body 35, thereby supporting the suspended region of the cap body 35, enhancing the pressure-bearing capacity of the cap body 35, and reducing the thickness requirement of the cap body 35.

[0186] The support column 37 has an inverted frustum-shaped structure, meaning that the dimension of the end of the support column 37 connected to the cap body 35 is larger than the dimension of the end of the support column 37 connected to the device layer 17. This causes the side of the support column 37 to extend inward from the cap body 35 to the device layer 17. When the cap body 35 is deformed under pressure, the connection between the cap body 35 and the periphery of the support column 37 is the point of maximum stress. The design of the support column 37 as an inverted frustum-shaped structure allows the stress at the point of maximum stress to be transmitted downward along the side of the support column 37, which can disperse the stress and reduce the risk of damage due to excessive stress at the point of maximum stress.

[0187] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for manufacturing a MEMS device, characterized in that, include: A substrate is provided, the substrate including a substrate layer, a device layer and a pre-embedded sacrificial layer located between the substrate layer and the device layer, the device layer having a groove to form a MEMS device structure, the groove penetrating the device layer along the thickness direction; A sacrificial layer is formed on the device layer, and the sacrificial layer fills the groove on the device layer; A capping layer is formed on the sacrificial layer, and a release hole is provided on the capping layer; By using the release hole to remove part of the sacrificial layer and part of the pre-embedded sacrificial layer, an encapsulation cavity covering the MEMS device structure is formed between the device layer and the capping layer, and the resonant structure of the MEMS device structure is suspended relative to the substrate layer. The encapsulation cavity is subjected to vacuum treatment to seal the release hole.

2. The method for manufacturing a MEMS device according to claim 1, characterized in that, The vacuum treatment of the encapsulation cavity includes: A getter is formed on the device layer; When the sacrificial layer is released, the getter fixed on the device layer is exposed, and the getter is activated to absorb air in the encapsulation cavity, so that the MEMS device structure is in a vacuum environment.

3. The method for manufacturing a MEMS device according to claim 2, characterized in that, The formation of a getter on the device layer includes: A metal adhesion layer is deposited on the device layer; A getter film is deposited on the metal adhesion layer to form a gas-absorbing film; An inert metal layer is deposited on the gas-absorbing film to obtain a gas-absorbing layer having a metal adhesion layer, a gas-absorbing film, and an inert metal layer; The getter layer is patterned to obtain multiple getters spaced apart on the device layer.

4. The method for manufacturing a MEMS device according to claim 1, characterized in that, The vacuum treatment of the encapsulation cavity includes: A getter is formed on the sacrificial layer; When the sacrificial layer is released, the getter fixed on the cap layer is exposed, and the getter is activated to absorb air in the encapsulation cavity, so that the MEMS device structure is in a vacuum environment.

5. The method for manufacturing a MEMS device according to claim 4, characterized in that, The formation of a getter on the sacrificial layer includes: An inert metal layer is deposited on the sacrificial layer; A getter film is deposited on the inert metal layer to form a getter film; A metal adhesion layer is deposited on the gas-absorbing film to obtain a gas-absorbing layer having an inert metal layer, a gas-absorbing film, and a metal adhesion layer; The getter layer is patterned to obtain multiple getters spaced apart on the sacrificial layer.

6. The method for manufacturing a MEMS device according to claim 1, characterized in that, include: Through-holes are formed by etching in the sacrificial layer, and the through-holes penetrate the sacrificial layer along the thickness direction; The capping layer is deposited on the sacrificial layer having the via, the capping layer including a capping body located on the side of the sacrificial layer away from the device layer, and a support post located within the via.

7. The method for manufacturing a MEMS device according to claim 6, characterized in that, The inner diameter of the top of the through hole is larger than the inner diameter of the bottom, so that the inner wall of the through hole extends inward from top to bottom, and the angle between the inner wall of the through hole and the bottom wall of the sacrificial layer near the device layer is less than or equal to 60°.

8. The method for manufacturing a MEMS device according to claim 6, characterized in that, include: The sacrificial layer is graphically processed to define the position and size of the encapsulation cavity.

9. The method for manufacturing a MEMS device according to claim 6, characterized in that, After forming the capping layer on the sacrificial layer, the method further includes: A contact hole is provided on the cap layer, and the contact hole penetrates the cap body and the support column along the thickness direction; A conductive layer is provided inside the contact hole and on the side of the cap body away from the device layer; A sealing film is formed on the cap body, the sealing film sealing the release hole and exposing the conductive layer.

10. The method for manufacturing a MEMS device according to claim 9, characterized in that, Also includes: A passivation layer is deposited on the sealing film, the passivation layer exposing the conductive layer; A reinforcing layer is formed by coating the surface of the passivation layer, and the thickness of the reinforcing layer is greater than the thickness of the passivation layer.

11. The method for manufacturing a MEMS device according to claim 1, characterized in that, The removal of a portion of the sacrificial layer and a portion of the pre-embedded sacrificial layer using the release hole includes: An etchant is injected through the release hole to remove the sacrificial layer corresponding to the location of the packaging cavity, the sacrificial layer located in the groove, and the pre-embedded sacrificial layer located below the MEMS device.

12. The method for manufacturing a MEMS device according to claim 1, characterized in that, The formation of a sacrificial layer on the device layer includes: A first sacrificial layer is formed on the device layer; A recess is provided on the first sacrificial layer, and the recess extends to the surface of the device layer; A second sacrificial layer is formed on the device layer at a position corresponding to the recess, and the thickness of the second sacrificial layer is less than the thickness of the first sacrificial layer.

13. The method for manufacturing a MEMS device according to claim 12, characterized in that, The cap layer includes a cap body and a protrusion located on one side of the cap body. The protrusion is located within the recess and extends to connect with the second sacrificial layer. The release hole penetrates the cap body and the protrusion. Removing part of the sacrificial layer and part of the pre-embedded sacrificial layer using the release hole includes: An etchant is injected through the release hole to remove the second sacrificial layer located below the protrusion by etching, thereby forming a release channel between the protrusion and the device layer; The corrosive agent removes a portion of the first sacrificial layer and a portion of the pre-embedded sacrificial layer located laterally outside the protrusion through the release channel.

14. The method for manufacturing a MEMS device according to claim 13, characterized in that, The sealing of the release hole includes: A sealing film is formed on the cap layer to cover and fill the release hole; wherein the sealing film includes a main body portion on the cap layer, a first sealing portion filling the release hole, and a second sealing portion located between the protrusion and the device layer, the second sealing portion sealing the release channel, and the second sealing portion being disposed at intervals on the outside of the MEMS device structure.

15. A MEMS device, characterized in that, It is prepared by the manufacturing method described in any one of claims 1-14.

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